Enhanced Wideband High Frequency (HF) Data Transmission with Adaptive Interference Avoidance

ABSTRACT

Methods, devices, and system for Enhanced Wideband HF data transmission with adaptive interference avoidance and other improvements. Several embodiments describe a mesh network comprising a plurality of transmitting and receiving nodes in a congested band. The network senses the interference spectrum occupancies at a plurality of receiver nodes and synthesizes transmit waveforms at the transmit nodes so that the spectra of the transmit signals fit into the gaps of the interference spectra at the receiver nodes. The waveform is based on FDM, including OFDM, with adaptive tone suppression at the transmitter. The spectrum occupancy information at each node is continually shared in the background among all nodes using a low data rate, Fountain code with erasure sensing at the receivers, which guarantees robust delivery.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 63/259,670, entitled “Enhanced wideband HF datatransmission with adaptive interference avoidance and otherimprovements” filed Aug. 04, 2021, the entire content of which is herebyincorporated by reference for all purposes.

BACKGROUND

The 3-30 MHz High Frequency (HF) band has been used from the earliestdays of radio communication. Despite revolutionary advances in otherradio technologies, HF has retained its value because it enablesbeyond-horizon communication links without satellites. The communicationlink may be provided by bouncing signals off the ionosphere, the mainlayers (D, E and F) residing approximately 50 - 450 km above the Earth’ssurface. The D layer is mainly an absorptive layer and is locallypresent mostly by day. The E and F layers are the main reflective layersand locally occupy different heights depending on the local time of day,supporting different path geometries. In addition to lower cost, thesurvivability of the ionosphere makes HF attractive to the military.

SUMMARY

The various aspects include methods of communicating data packetsthrough a wireless communication network, which may include receiving,by a transceiver device from a receiver device, spectrum occupancyattributes of narrowband interference on a communication channel at alocation of the receiver device, and transmitting, from the transceiverdevice to the receiver device, a data packet using a waveform generatedbased on the spectrum occupancy attributes of the narrowbandinterference on the communication channel at the location of thereceiver device.

In some aspects, transmitting the data packet using the waveformgenerated based on the spectrum occupancy attributes of the narrowbandinterference on the communication channel at the location of thereceiver device may include transmitting the data packet using afrequency division multiplexed waveform including a plurality ofsubcarriers and suppressing at least some of the subcarriers fromtransmission based on the spectrum occupancy attributes of thenarrowband interference on the communication channel, and assigning userdata to be carried only by the transmitted subcarriers. In some aspects,transmitting the data packet using the frequency division multiplexedwaveform including the plurality of subcarriers may include transmittingthe data packet using a frequency division multiplexed waveform thatincludes a plurality of mutually orthogonal subcarriers, in which eachof the mutually orthogonal subcarriers is modulated with a subset of thedata contained in one transmit interleaving block.

In some aspects, the methods may further include applying power saved bysuppressing the subcarriers towards transmitting the subcarriers thathave not been suppressed. In some aspects, transmitting the data packetusing the waveform generated based on the spectrum occupancy attributesof the narrowband interference on the communication channel at thelocation of the receiver device may include selecting a modulation andcoding scheme for each transmitted subcarrier based on an interferencepower within spectrum occupied by the subcarrier at the receiver device.In some aspects, transmitting the data packet using the waveformgenerated based on the spectrum occupancy attributes of the narrowbandinterference on the communication channel at the location of thereceiver device may include generating the waveform based on thespectrum occupancy attributes of the narrowband interference on thecommunication channel at the location of the transceiver device.

In some aspects, the methods may further include determining, by thetransceiver device, spectrum occupancy attributes of narrowbandinterference on the communication channel at the location of thetransceiver device, and broadcasting, by the transceiver device, thedetermined spectrum occupancy attributes for reception by one or moreother devices. In some aspects, determining the spectrum occupancyattributes of the narrowband interference on the communication channelmay include sensing the power spectral density of the narrowbandinterference during a period of radio silence, and generating a spectrumusability mask from the sensed power spectral density. In some aspects,determining the spectrum occupancy attributes of narrowband interferenceon the communication channel at the location of the receiver device mayinclude computing a power spectral density of the waveform based on adiscrete Fourier transform (or based on a fast Fourier transform) andgenerating a spectrum usability mask by quantizing the power spectraldensity relative to a set of threshold values. In some aspects,generating the spectrum usability mask by quantizing the power spectraldensity relative to the set of threshold values may include identifyinga threshold level of interference power received by a known subcarrierthat is not exceeded when averaged over a known period of time. In someaspects, generating the spectrum usability mask by quantizing the powerspectral density relative to the set of threshold values may includeidentifying upper and lower threshold limits of interference powerreceived by a known subcarrier such that, when the interference power isaveraged over a known period of time, a value of the averageinterference power is bounded by the upper and lower threshold limits.

In some aspects, the methods may further include generating ademodulated data set by demodulating modulated data carried bysubcarriers in the waveform, and erasing data carried by the subcarriersof the waveform that include cochannel interference. In some aspects,the methods may further include generating a demodulated data set bydemodulating modulated data carried by subcarriers in the waveform,determining whether the demodulated data set includes a demodulated datapacket that includes an uncorrected error, and erasing the demodulateddata packet in response to determining that the demodulated data setincludes the demodulated data packet that includes the uncorrectederror. In some aspects, the methods may further include identifyingpackets that are free of errors, maintaining a first count of the numberof packets received in the receiver device, and maintaining a secondcount of the number of packets received error free in the receiverdevice.

In some aspects, the communication channel may include a plurality ofdiscontiguous subchannels in the radio spectrum (the subchannels havingarbitrary bandwidths), and the methods may further include aggregating,by a transceiver device, the plurality of discontiguous subchannels toform a contiguous channel at an intermediate frequency. In some aspects,the intermediate frequency in the transceiver device may be zero (0) Hz,and the signals may be represented in the transceiver device in complexbaseband form.

Further aspects may include methods of communicating a file including afinite number of source data packets through a frequency divisionmultiplexed wireless communication channel that is partially occupied bynarrowband interference, which may include using, by a transceiverdevice, a fountain code to encode the source data packets, transmitting,by the transceiver device to a receiver device, the encoded data packetsusing all subcarriers, regardless of whether they are encounteringinterference at the receiver, and continuing to transmit, by thetransceiver device to the receiver device, the encoded packets until anotice of acknowledgement of file delivery or a notice of failure offile delivery is received.

In some aspects, the methods may further include receiving encoded datapackets, identifying the received packets that are free of errors,keeping a first count of the number of received packets, and keeping asecond count of the number of the received packets that are free oferrors. In some aspects, the methods may further include decoding thefile of transmitted encoded data packets in response to determining thatthe second count exceeds a threshold. In some aspects, the methods mayfurther include abandoning the decoding attempts for the file inresponse to determining that the first count exceeds a threshold value.

In some aspects, the methods may further include erasing a receivedpacket based on spectrum occupancy attributes of narrowband interferenceon a communication channel at a location of the transceiver device. Insome aspects, the methods may further include performing a cyclicredundancy check test on a demodulated packet, and erasing thedemodulated packet in response to determining that the demodulatedpacket failed the cyclic redundancy check test.

In some aspects, the file may include information about the spectraloccupancy of interference received by the transceiver device, and themethod may further include broadcasting spectral occupancy informationfor reception by a plurality of other transceivers. In some aspects, thefile may further include user data, and the method may further includebroadcasting the file for reception by a plurality of receivingtransceivers having dissimilar interference spectral occupancies attheir locations.

Further aspects may include a transceiver device configured to performvarious operations corresponding to the methods discussed above.

Further aspects may include a computing device (or transceiver device)having a processor configured with processor-executable instructions toperform various operations corresponding to the methods discussed above.

Further aspects may include a non-transitory processor-readable storagemedium having stored thereon processor-executable instructionsconfigured to cause a processor to perform various operationscorresponding to the method operations discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and together with the general description given above and thedetailed description given below, explain the features of the invention.

FIG. 1 is a signal spectrum diagram that illustrates an examplemulticarrier orthogonal frequency division multiplexed (OFDM) waveformthat could be generated to include a spectrum occupancy that adaptivelyavoids the spectrum occupancy of the interference in accordance withsome embodiments.

FIG. 2 is a table diagram that illustrates a table that could be usedfor the identification of subcarriers (SC) by an identification (ID)number in accordance with some embodiments.

FIG. 3 is a table diagram that illustrates a table that could be usedfor the identification of subcarriers (SC) by its transmissionfrequency, referenced to the left (lower frequency) edge of the nominal(40.040 kHz bandwidth) channel.

FIG. 4 is a table diagram that illustrates a table that could be used toindicate that, out of the 364 subcarriers, two sets of 13 subcarriers(batch 1 and batch 2 shown shaded) may be dedicated to broadcasting thereceiver’s SUM data.

FIG. 5 is a component diagram that illustrates an example of subcarriersuppression, responsive to the fine spectrum occupancy at the receiver,and a frequency domain representation of the occupied spectrum.

FIG. 6 is a component block diagram that illustrates an examplecommunication device in the form of an E- wideband high frequency (WBHF)transmitter that could be configured to implement some embodiments.

FIG. 7 is a component block diagram that illustrates an examplecommunication device in the form of an E-WBHF receiver that could beconfigured to implement some embodiments.

FIG. 8 is a component block diagram that illustrates an examplesub-system of a E-WBHF receiver for receiving and assessing SUM data.

FIG. 9 is an illustration of an example of a [G] matrix that could begenerated in some embodiments.

FIGS. 10 and 11 are component block diagrams that illustrate randomlinear fountain code blocks in accordance with some embodiments.

FIG. 12 is a process flow diagram that illustrates a method ofprocessing packets for transmission in accordance with some embodiments.

FIG. 13 is a process flow diagram that illustrates a method ofprocessing packets for reception in accordance with some embodiments.

FIG. 14 is a process flow diagram that illustrates a method ofcommunicating data packets through a wireless communication network inaccordance with some embodiments.

FIG. 15 is a process flow diagram that illustrates a method ofcommunicating a file that includes a finite number of source datapackets through a frequency division multiplexed wireless communicationchannel that is partially occupied by narrowband interference inaccordance with some embodiments.

FIG. 16 is a component block diagram illustrating an example system onchip (SOC) that could be configured to implement the variousembodiments.

FIG. 17 is a component block diagram illustrating an example servercomputing device that could be configured to implement the variousembodiments.

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.References made to particular examples and implementations are forillustrative purposes and are not intended to limit the scope of theinvention or the claims.

In overview, the various embodiments include methods, and components(e.g., computing device, transceiver, transmitter, receiver, modemprocessor, etc.) configured to implement the methods, for wirelesslycommunicating information (e.g., a file, data packets, etc.). In someembodiments, the information may be communicated over a high frequency(HF) channel (i.e., 3-30 MHz), which may be partially occupied bynarrowband interference. Some components may be configured to mitigatethe negative impacts of the narrowband interference by generating,encoding, transmitting, receiving, and/or decoding a waveform thatincludes a spectrum occupancy that adaptively avoids the spectrumoccupancy of the interference. The use of such a waveform may reducetransmit power and/or increase throughput (compared to systems do notadapt to the spectrum occupancy of the interference at the receiver).

In some embodiments, the waveform may be a frequency divisionmultiplexed waveform in which some of the subcarriers may be suppressedfrom transmission based on a spectrum usability mask. The power saved bysuppressing subcarriers may be applied towards transmitting subcarriersthat have not been suppressed.

In some embodiments, the components may be configured to determine themodulation and coding used for each subcarrier based on the interferencepower within the spectrum occupied by the subcarrier. In someembodiments, the components may be configured to identify and erase datafrom subcarriers that include co-channel interference power that isabove a threshold value. In some embodiments, the components may beconfigured to identify and erase data packets that include uncorrectederrors.

In some embodiments, the components may be configured to use a fountaincode to encode data packets and transmit the encoded data packets usingall subcarriers (regardless of whether they are encounteringinterference at the receiver) until the number of error free packetsreceived at the receiver exceeds a threshold value. The receiver maymaintain a count of the total number of packets received and a count ofthe number of error free packets received, which may be communicatedback to the transmitter.

For ease of reference, some embodiments are described with reference toa transmitter or receiver. However, it should be understood that any orall of the embodiments discussed in this application may be implementedin a transceiver device or node that includes a transmitter, receiver,and/or transceiver, any or all of which may be included in or coupled toone or more processors (e.g., modem processor, applications processor,vector coprocessor, etc.).

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any implementation described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other implementations.

The phrase “narrowband interference” may be used herein to refer toinstances of high frequency (HF) interference where congestion ismaterially less than 100%, for example, less than 75%. In other words,the interference is considered narrowband if, when observed through a100 Hz bandwidth measurement bandwidth, or subband, over a contiguousspan of at least 1 kHz, the power levels in at least 25% of the subbandsare less than a threshold power value that is 10 dB above theatmospheric noise.

The term “maximum usable frequency (MUF)” may be used herein to refer tothe highest radio frequency that can be used for transmission betweentwo points via reflection from the ionosphere (skywave propagation) at aspecified time, independent of transmitter power.

The term “optimum working frequency (OWF)” may be used herein to referto an estimate of the maximum frequency that may be used for a givencritical frequency and incident angle. A communication device may usethe OWF to avoid the irregularities of the local atmospheric conditions.Predictions of OWF versus communication range are published by variousagencies and are used for high frequency (HF) frequency planning, bothin offline applications and automatic link establishment (ALE) softwaretools. The OWF predictions may depend on both the geographic region andthe sunspot number. The latter has a 11-year cycle and represents thelongest-term determinant of HF channel characteristics.

The ionosphere is the ionized part of the upper atmosphere of Earth,which influences radio propagation to distant places on Earth. Theionosphere is not static, and as a result, the high frequency (HF)channel (i.e., 3-30 MHz) may undergo short, medium, and long-termvariations. Due to these variations, it is often challenging to use theHF channel as a communication medium.

Short-term time variations in the HF channel may arise from fading (timevarying) multipath propagation. Ionospheric multipath may cause timedispersion of the order of 2 - 6 ms, and frequency dispersion, which maymanifest as fading, in the range of 1 - 5 Hz. Multipath may be caused bythe reflected rays taking different paths through the ionosphere. Fadingmay be caused by turbulence in the ionospheric layers.

Medium-term variations in the HF channel may be caused by diurnalchanges in the heights and transmission characteristics of theionospheric layers. The changes may be caused by changing solarradiation - greater radiation during the day increases ionization. Theheights and ionization levels of the layers may determine the MUF ormaximum frequencies that may support reflection. A slightly lowerfrequency (e.g., OWF) may be used as the practical upper bound for agiven communication range, with the availability of the frequency beingguaranteed for 90% of days.

In addition to time and frequency dispersion, the HF channel mayexperience severe congestion in many parts of the world, especially atnight, with many users contending for the same frequency band. There areseveral reasons for this HF band congestion. In most other bands, themean propagation characteristics (measured by pathloss) are morepredictable. This enables frequency spectrum to be allocated toindividual users/operators, and to be enforced by regulators. However,at high frequency, for a given geographic region, the propagationcharacteristics may change drastically with time of day, season, andyear in the sunspot cycle. This makes managing enforceable frequencyspectrum allocations difficult. The International TelecommunicationUnion (ITU) standards subdivide the high frequency band into allocationsby user type (e.g., fixed, mobile, aeronautical, etc.) to keep similartypes of users in common subbands. However, there is no ‘allocation’ ofa subband exclusively to one operator, as in cellular systems. Users ina common subband contend for spectrum based on transmit power andprotocol power efficiency. Consequently, it is difficult to distinguishan interfering signal originating from few hundred kilometers away froman interfering signal originating from thousands of kilometers away.

HF band congestion may be exacerbated by the fact that, at night, theOWF (for a given range) reduces to a fraction of its value by day. Forexample, the HF spectrum occupancy, observed through a 1 kHz measurementbandwidth, may shrink from 30 MHz and above during the day to underapproximately 15 MHz at night. See e.g., Gott, G. F., Dutta, S. andDoany, P., “HF Interference with application to digital communications”,IEE Proceedings, Vol. 130, Pt. F, No. 5, August 1983, the contents ofwhich are incorporated herein by reference for all purposes.

For voice and data communication, the HF channel has traditionally beenchannelized in 3 kHz standard allocations by the ITU. For an optimalwaveform design, as is provided by the various embodiments, it is usefulto understand the spectral characteristics of other user interferenceinside the allocated 3 kHz band, measured with a spectral resolutionthat is substantially finer than 3 kHz.

Research into HF spectrum occupancy has influenced the choice ofoccupancy definitions. University of Manchester Institute of Science andTechnology (UMIST) has used 100 Hz resolution, or measurement bandwidth,to characterize spectrum occupancy inside a 3 kHz window, which may bereferred to herein as “fine spectrum occupancy.” In contrast, spectrumoccupancy measured with a 3 kHz measurement bandwidth may be referred toas “coarse spectrum occupancy.” The latter term may also be used forspectrum occupancy measured with 1 kHz measurement bandwidth(statistically, there is not much difference between the twoparameters).

Research into fine spectrum occupancy has revealed the following salientcharacteristics. See e.g., Gott, G. F., Dutta, S. and Doany, P., “HFInterference with application to digital communications”, IEEProceedings, Vol. 130, Pt. F, No. 5, August 1983; S. Dutta and Gott,G.F., “Correlation of HF interference spectra with range”, IEEProceedings, Vol. 128, Pt. F, No. 4, August 1981; Gott, G. F., Wong, N.F., and S. Dutta, “Occupancy Measurements across the entire HFSpectrum,” Propagation Aspects Of Frequency Sharing Interference AndSystem Diversity, ed. H. Soicher, March 1983; Stehle, R. H., and Hagn,G. H., “HF channel occupancy and band congestion: The other-userinterference problem”, Radio Science, Volume 26, No. 4, pp 959 - 970,August 1991; and Gott, G. F. and Green, P. R., “The Measurement AndModelling Of Hf Spectral Occupancy Over Northern Europe Using A MonopoleAntenna, 1990 -2001”, University of Manchester report, August 2007, thecontents all of which is incorporated herein by reference for allpurposes. Fine spectrum occupancy may be non-uniform within a 3 kHz and1 kHz band (i.e., the interference may be predominantly narrowbandrelative to a 1 kHz or 3 kHz window). When other users are absent, thebackground noise floor may be determined based on atmospheric noise,which is spectrally white over 50 kHz (with a slow, downward frequencygradient over the HF band).

Examples of 50 kHz segments of the HF band recorded in England in 1980during midnight and midday show that, at midnight, when the voiceband (3kHz bandwidth) availability of the band, sliced 10 dB above theatmospheric noise floor, is close to zero, the Availability of 100 Hzsubbands is nearly 50% (Congestion is 0.58). See e.g., Gott, G. F.,Dutta, S. and Doany, P., “HF Interference with application to digitalcommunications”, IEE Proceedings, Vol. 130, Pt. F, No. 5, August 1983,the contents of which are incorporated herein by reference for allpurposes. In contrast, during midday, the Congestion is only 0.17 withthe availability being defined as (1 - Congestion). In congestedconditions, other-user interference may be narrowband relative to a 1 or3 kHz spectral window.

The above observations have motivated the waveform designs of many ofthe present embodiments. They offer an opportunity for shaping thetransmit waveform’s spectrum to avoid the peaks of the interferencepower spectral density at the receiver.

Research has also revealed the following additional characteristics ofHF interference, which are also relevant to the design of the waveformsand protocols of the various embodiments. The spectrum occupancy may betime stationary over minutes - sometimes hours. See e.g., S. Dutta andGott, G.F., “Correlation of HF interference spectra with range”, IEEProceedings, Vol. 128, Pt. F, No. 4, August 1981, the contents of whichis incorporated herein by reference for all purposes. Further, thespectrum occupancy may be spatially correlated with distance overseveral hundred kilometers. While the former stems from the usagepatterns of HF users, the latter arises from the Earth -ionospheregeometry. See id.

As background, the earliest forms of HF communications included Morsecode and single sideband (SSB) analog voice, in addition to short waveamplitude modulation (AM) broadcasting. HF communications usageprogressed to low rate (75 bps) frequency-shift keying (FSK)transmission in a 3 kHz channel for connecting teletype terminals. Foranalog transmission, coping with channel fading was limited to selectinga frequency close to the OWF, which typically encountered less timedispersion than at lower frequencies, and using time/frequency diversitytechniques. However, competition for near-OWF frequencies may be severe,and to avoid congestion, a suboptimal lower frequency was often used.

Historically, more spectrally efficient, multiple-tone (also referred toas ‘parallel tone’, or simply ‘parallel’) modems were developed. Oneknown parallel modem was Kinneplex, referred to in the US military asLink-11. The waveform structure was multicarrier, orthogonal frequencydivision multiplexed (OFDM), differential quaternary phase-shift-keying(DQPSK), assisted by a 605 Hz Doppler correction pilot tone. The use ofmulticarrier OFDM provided a quantum leap increase in the spectralefficiency of the link over conventional solutions at the time, creatingone of the first instances of 2.4 kbps data transmission over 3 kHzbandwidth at HF. The option existed to double the occupied bandwidthusing double sideband suppressed carrier (DSB/SC) modulation at thetransmitter (transmitting the same information in the lower sideband(LSB) and upper sideband (USB)), and independent sideband (ISB)demodulation at the receiver with frequency diversity combining. Thismitigated frequency selective fading, which is typical on HF channelswith 3 kHz frequency bandwidth.

Research has demonstrated the potential for link optimization byadapting to the fine structure of HF interference spectrum. However, asdescribed below, no wideband HF data modem has yet been proposed thatadapts to the fine structure of interference spectrum occupancy. Somesolutions have developed several narrowband, relatively low data rate HFcommunication systems (transmitting 75 bps over 3 kHz bandwidthchannels), exploiting the fine structure of HF spectrum occupancy.However, none of these solutions adapted the waveforms and protocols ofan HF communication system to interference spectrum occupancy forchannel bandwidths substantially greater than 3 kHz and data rates inthe order of hundreds of kbps. As explained in more detail below,occupancy statistics indicate that such adaptation may reduce thetransmit power of a WBHF link by approximately 20 dB.

It should be apparent to those skilled in the art that, when the bearerdata rate is of the order of hundreds of kbps, as mentioned above,applications other than data communication may be feasible, such asdigitized voice and compressed video. Therefore, the reference to “datapackets” should be interpreted as packets of bearer channel data, notapplication layer data.

Coarse HF spectrum occupancy recorded in England circa 1980 has showncongestion for different measurement bandwidths and interference powerslicing thresholds. See e.g., Gott, G. F., Wong, N. F., and S. Dutta,“Occupancy Measurements across the entire HF Spectrum,” PropagationAspects Of Frequency Sharing Interference And System Diversity, ed. H.Soicher, March 1983 and Gott, G. F. and Green, P. R., “The MeasurementAnd Modelling Of Hf Spectral Occupancy Over Northern Europe Using AMonopole Antenna, 1990 -2001”, University of Manchester report, August2007, the contents of both are incorporated herein by reference for allpurposes. It was observed that changing the congestion of a 3 kHzchannel from 99% to 45% required changing the interference threshold by20 dB (between -107 dBm and -87 dBm), which may require changing thetransmit power by 20 dB. In some instance, by using the methods taughthere, in which it were possible to operate in a 99% congestedenvironment with the same packet error rate as in a 45% congestedenvironment, 20 dB of transmit power saving may accrue. Analysis of thefine structure of the interference showed that, when the band is closeto 100% occupied when viewed through a 3 kHz window, it is often only50% occupied when viewed through a 100 Hz window. The variousembodiments disclosed herein implement interference-adaptive methods torealize this potential for improved power efficiency, which may beexchanged for greater throughput for a given transmit power.

More recently, HF modem technology has moved away from the parallelmodems like Link-11 to single tone modems exemplified byMIL-STD-188-110C which, instead of transmitting data in separateparallel streams on multiple narrowband subcarriers, transmitted themserially on a single, wider bandwidth carrier. Hence, they are alsoreferred to as serial modems. MIL-STD-188-110C represents the presentstate of the art of present wideband HF (WBHF) data communicationsystems.

In WBHF, adaptive equalization may be used to combat time and frequencydispersion. The apparent motivation for this shift away from parallelmodems (such as Link-11) was that parallel tones create a high peak toaverage power ratio (PAPR) in the composite waveform, which is much lessfor a serial modem. However, the PAPR difference between a quadratureamplitude modulation (QAM) serial modem and a parallel modem with manytones is expected to be only of the order of 6 dB, citing the differencebetween single frequency FDM (DFT-S-OFDM) and CP-OFDM among 3GPPcellular waveforms. Further, the state of the art of digital signalprocessors enabled realization of sophisticated channel equalizers,providing additional incentive for realizing serial modems, which werenot previously feasible. Conspicuous by its absence in the “problemstatement for HF modems” was any recognition of the non-white nature ofinterference from other users.

Some embodiments disclosed herein may include components (e.g., WBHFmodems, etc.) configured to optimize the HF communication link for bothtime-frequency dispersion and non-white interference.

Some embodiments disclosed herein may include components that areconfigured to implement a new WBHF communication system withInterference Avoidance (Enhanced WBHF, or E-WBHF). For brevity and tofocus the discussion on the most important features, certain coreprinciples implemented by the various embodiments are explained throughan example design. This example design is sometimes referred to as a‘preferred embodiment’. However, other designs may be used to implementthe core principles. As such, nothing in this application should be usedto limit the scope of the claims to the example design or preferredembodiment unless expressly recited as such in the claims.

The E-WBHF modem may preserve the upper layers of the above-describedstandard as much as possible, and substantially improve the powerefficiency of the waveform by dynamically adapting the spectrum of thetransmitted waveform to the spectral density of other user interferenceat the receiver. In some embodiments, the sum of the desired signal andinterference spectral densities at the receiver may be a constant.

In the various embodiments, the E-WBHF modem may include the attributesdescribed below.

Waveform

In the preferred embodiment, the waveform used is OFDM, althoughnon-orthogonal FDM may also be used in alternate embodiments. Theorthogonality of the FDM subcarriers in OFDM may not be material in someembodiments. In some embodiments, E-WBHF may selectively suppresscertain OFDM subcarriers, including none, to adapt the transmittedwaveform’s spectrum to the fine spectrum occupancy at the receiver. Insome embodiments, fine spectrum occupancy may be defined to have ameasurement bandwidth of 110 Hz, and coarse spectrum occupancy to have ameasurement bandwidth of 3 kHz.

All subcarriers may be located in frequency on a common raster with 110Hz spacing. Suppressing subcarriers at the transmitter may savetransmitter power, which may be applied to transmitted subcarriers thathave not been suppressed, thereby keeping the mean transmitted powersubstantially constant regardless of the number of subcarrierstransmitted. In certain modes of operation, such as unicast (point topoint transmission), some of the subcarriers in the transmitted signalmay be suppressed. In other modes, such as broadcast or multicast(referred to generally as ‘broadcast’ in this disclosure) allsubcarriers may be transmitted.

FIG. 1 illustrates a preferred embodiment that uses a multicarrier OFDMwaveform 100. In the example illustrated in FIG. 1 , there are threehundred and sixty four (364) subcarriers (SCs) situated on the abovefrequency raster, with a numerology described below. The subcarriers,shown with solid outlines 102, are transmitted, while subcarriers withdotted outlines 104 are suppressed (not transmitted), responsive to adetermination by the system that, at the intended receiver location, thespectra corresponding to subcarriers 104 are occupied by excessiveinterference.

The waveform has a nominal channel bandwidth of 40.04 kHz and an ITUallocated bandwidth of 48 kHz, corresponding to sixteen 3-kHz standardHF channels. In comparison, the WBHF standard uses eight standard 3-kHzchannels, comprising 24 kHz. The spectrum allocation to the presentembodiment of E-WBHF may be doubled because, in highly congested bands,the availability of a 110 Hz subband is about 0.5.

Although, as described above, the fine spectrum occupancy may bemeasured with 100 Hz measurement bandwidth, the preferred embodiment mayuse 110 Hz for the same metric to fit the numerology of its OFDMwaveform design. This minor difference may not have a significant impacton the measured spectrum occupancy characteristics. Further, smalldeviations from 110 Hz or 100 Hz, in the choice of the measurementbandwidth for fine spectrum occupancy, do not reduce, negate, orinvalidate the benefits provided by the various embodiments.

The key parameter defining “narrowband interference”, in the context ofthe present application, and thereby fine versus coarse spectrumoccupancy, is the ratio of the measurement bandwidths used for fine andcourse spectrum occupancy. The ratio of 3 kHz and 100 Hz is 30. The useof any ratio above 10, corresponding to 300 Hz in a 3 kHz allocation,could also derive benefits from the various embodiments.

Various embodiments described herein assume that the 16 standard (3 kHz)channels are adjacent and contiguous. Other embodiments maycarrier-aggregate non-contiguous standard HF channels by converting eachto complex baseband, using a parallel multi-channel tuner, and placingthem adjacent to each other to create an objective spectrum plan.

The preferred embodiment may use non-contiguous carrier aggregation,which may offer the advantage of pre-selecting less congested standardchannels to synthesize the objective waveform. As an example, thestandard 3-kHz bandwidth channel (elementary channel) may be in acongested part of the HF band at night. Accordingly, the elementarychannels may be selectively placed in the HF band to avoid the peaks ofthe coarse spectrum occupancy (measured with 3 kHz bandwidth). Suchplacements are necessarily non-contiguous, and in the above example, mayyield 24 kHz of relatively less congested spectrum. In some embodiments,the less congested spectrum may be processed to further improve ormaximize spectrum utilization through the methods taught here to exploitnon-uniform, interference power spectral density.

During day-time, most of the spectrum may have little interference. Assuch, selective placement of the elementary channel may be redundant.Invoking elementary channel preselection may be an implementationchoice.

Waveform Numerology

In OFDM, the following parameters are referred to as the ‘numerology’ ofthe waveform. Provided below is the numerology of the preferredembodiment. They are informed by the numerology of Link-11, and havebeen proven suitable for use in the HF channel.

Frame length (symbol period + CP): 13.33 ms

Symbol period: [9.09 ms]

Cyclic Prefix (CP): [4.24 ms]

Subcarrier spacing 110 Hz. Depending on the spectrum occupancy at thereceiver, not all subcarriers are transmitted - some are suppressed atthe transmitter.

This waveform may transmit data on each subcarrier at (⅟9.09E-3 = 75symbols/s). The net throughput may be the aggregate of the data on allsubcarriers. The inverse relation between the symbol period of 9.09 msand subcarrier spacing of 110 Hz may ensure orthogonality between thesubcarriers. Such a requirement may not exist for non-orthogonalfrequency division multiplexing, which may be used in some embodiments.

For a given transmit power and pathloss, based on thesignal-to-noise-and-interference power ratio (SNIR) in the subcarrierbandwidth at the receiver, different throughput rates may be achieved byusing different modulation and coding schemes, collectively referred toas ‘MODCODE’. While it may be preferable to select clear subchannels(limited only by atmospheric noise), in highly congested bands,subchannels with limited amounts of interference power may also beutilized. The exchange of spectrum occupancy data among the nodes,referred to as spectrum usability mask (SUM), may enable the use ofoptimal transmit power and MODCODE on each subcarrier, responsive to theinterference spectral density in the subcarrier spectrum at the locationof the receiver. In some embodiments, these resource choices may be madeby a resource manager in the transmitter. In some embodiments, theresource management scheme may be customized to specific missions andimplementation.

Modulation and Coding

In the preferred embodiment, different MODCODEs may be used in differentoperational modes, which include user data unicast, user data broadcastand SUM data broadcast.

To reuse existing technologies, in the unicast mode, forward errorcorrection (FEC) coding and the modulations may be preserved relative tothe legacy WBHF standard. The modulation may be coherent, quadratureamplitude modulation (QAM), including the multiple phase shift keying(MPSK), further including binary phase-shift keying (BPSK) andquadrature phase-shift keying (QPSK). Maintenance of phase coherence atthe receiver may be assisted by embedded, time multiplexed, pilotsymbols. A balance may be maintained between user plane capacity and theefficacy of mitigating time and frequency dispersion of the channel byoptimally apportioning power to pilot and traffic signals.

The FEC scheme for unicast transmission may be similar to WBHF (rate-½,k=7 and k=9, tail-biting, punctured convolutional code). However, twomajor differences may be introduced in E-WBHF relative to WBHF.

First, erasure detection may be used in the convolutional decoder, whichmay improve performance relative to erroneous symbols being input to thedecoder. Erasures may be declared at the receiver when a subcarrier’sfrequency is observed to contain excessive interference, the observationbeing made through fine spectrum analysis of the received signal duringperiods of radio silence enforced by the protocol.

Second, a fountain code may be used to share spectrum usability mask(SUM) data with other nodes in the network. As explained in more detailbelow, a fountain code may assure, with very high confidence, that allnodes have error free copies of the SUM data of every node of thenetwork. This may be a foundational requirement. The SUM data mayrepresent a quantized version of the fine spectrum occupancy at thereceiver location.

An advantage of using a fountain code to distribute SUM data is that thelatter changes very slowly with time, and the reliability of a fountaincode to transport a finite data block, or file, goes up exponentiallywith time. This may not be true of more common FEC codes transportingstreaming (endless) data.

In the preferred embodiment, in addition to usage for exchanging SUMdata, the fountain code may also be used for long-range broadcasttraffic, where the receivers are at a distance greater than a minimumlimit, such as 300 km, beyond which range the interference spectrumoccupancy is typically uncorrelated. The transmission scheme forbroadcast traffic may be changed relative to unicast traffic because, inlong range broadcast, the transmit spectrum may not be shaped to fit asingle objective mold, given that the interference spectrum occupancy isnot guaranteed to be correlated at all receiver locations. However, forbroadcast traffic networks under 300 km range, transmit waveformspectrum shaping fitted to the interference spectrum received at thetransmitter may be used because of the high likelihood of correlatedinterference spectra at the transmitter and receiver. This may be ofconsiderable benefit to short-range (both surface wave and high-angleskywave) HF links, which are often used in military missions. Forexchanging SUM data in networks where the maximum range is approximately300 km, transmit waveform spectrum shaping fitted to the interferencespectrum received at the transmitter may also be used, as discussedabove for broad

Where knowledge of interference spectrum occupancy at the receiver isnot available to the transmitter, a fountain code may offer an alternatemethod, based on coding rather than physical layer changes, of adaptingto unknown narrowband interference at the receiver. Additional detailsof applying fountain codes in accordance with various embodiments areprovided further below.

Interleaving

Block interleaving may be used to achieve frequency and time diversity,optimally matched to HF channel characteristics related to bothinterference and fading. It should be understood that the design exampleprovided herein is exemplary, not mandatory, towards implementing thevarious embodiments.

In the preferred embodiment illustrated in FIGS. 2 and 3 , there are 364subcarrier frequencies, occupying a total of 364x110=40,040 Hz. Eachcell of the interleaving block (IL Block) may contain a symbol, whichmay be a digital word representing the complex amplitude of the signalin each 13.33 ms epoch. For example, in instances in which 64 QAM wasselected in the MODCODE scheme, the word would have 6 bits, excludingany error detection and correction bits. A total of up to 364 symbolsmay be transmitted simultaneously in each epoch -- fewer symbols aretransmitted in instances in which certain subcarriers are suppressed toavoid narrowband interference at the receiver.

FIG. 2 identifies the subcarrier (SC) (represented by a cell of the ILBlock) by an identification (ID) number, which ranges from SC-1 toSC-364. FIG. 3 identifies the subcarrier by its transmission frequency,referenced to the left (lower frequency) edge of the nominal (40.040 kHzbandwidth) channel. The left edge of the first subcarrier is designated0 Hz. In FIGS. 2 and 3, 364 parallel tones, or subcarriers, are shown,occupying a total bandwidth of 40,040 Hz.

FIG. 4 illustrates that, out of the 364 subcarriers, two sets of 13subcarriers (batch 1 and batch 2 shown shaded) may be dedicated tobroadcasting the receiver’s SUM data - they make up the SUM channels.

FIG. 5 illustrates an example of subcarrier suppression, responsive tothe fine spectrum occupancy at the receiver, the suppressed subcarriersbeing shaded; a frequency domain representation of the occupied spectrumis also depicted. Because the interference is narrowband, the shadedsubcarriers are clustered.

FIG. 6 illustrates an example communication device in the form of anE-WBHF transmitter 600 that could be configured to implement someembodiments. In the example illustrated in FIG. 6 , the E-WBHFtransmitter 600 includes a data source 602, a traffic convolutionalencoder 604, a traffic fountain encoder 606, a bit-to-serial mapper 608,a transmit block interleaver 610, a serial to parallel mapper 612, anOFDM modulator 614, a transmitter 616, an antenna coupler 618, anantenna 620, a receive subsystem 622, a receive block interleaver 624,SUM data receivers/decoders 626, 628, and a SUM database 630. FIG. 6 isdescribed in more detail further below.

FIG. 7 illustrates an example communication device in the form of anE-WBHF receiver 700 that could be configured to implement someembodiments. In the example illustrated in FIG. 7 , the E-WBHF receiver700 includes an antenna 702, an antenna coupler 704, a receiver 706, anOFDM demodulator 708, parallel to serial mapper 710, receive blockinterleaver 720, symbol to bit mapper 722, traffic convolutional decoder724, traffic fountain decoder 726, data sink 728, SUM datareceivers/decoders (626, 628), and a SUM database 630. FIG. 7 isdescribed in more detail further below.

FIG. 8 illustrates an example sub-system of a E-WBHF receiver thatincludes an antenna 802, receiver subsystems 804, block interleaver 806,other-node SUM data receiver 810, a SUM symbol extractor 812, SUM symbolerror detector and corrector 814, error free SUM symbol collector 816,SUM data decoder 818, G-matrix Generator and Inverter 820, other-nodeSUM data storage, own-node SUM data assessor 824 that includes a powerspectral density threshold slicer 826, SUM data encoder 828, andown-node SUM data storage 830.

FIG. 9 illustrates an example of a [G] matrix that could be generated(e.g. by the G-matrix Generator and Inverter 820) in some embodiments.

FIG. 10 illustrates a random linear fountain code encoder block 1000,which includes an input interleaving block 1002, a G-matrix generator1004, an inner product 1006 and an output interleaving block 1008.

FIG. 11 illustrates a random linear fountain code decoder block 1100,which includes a received interleaving block 1102, an inverse ofG-matrix generator 1104, an inner product 1106 and decoded interleavingblock 1108.

With reference to FIGS. 2-11 , symbols received time-sequentially fromthe data source 602 may be read into an interleaving block (IL Block) bycolumns and read out to the rest of the transmit chain by rows (i.e.,symbols in a row are sent in adjacent time slots). As shown in FIGS. 2and 3 , time-adjacent symbols (e.g. SC-1, SC-15, SC-29, etc.) aremutually offset in frequency by 1540 Hz. This means that, at the inputto the convolutional decoder (e.g., traffic convolutional decoder 724illustrated in FIG. 7 ) in the receiver, where the received symbols areread out by rows from an identical block interleaver, the demodulatedsymbols would have been carried on subcarriers separated byapproximately 1540 Hz. This frequency offset is desirable both in termsof the correlation statistics of fine spectrum occupancy and thecoherence bandwidth of the HF channel, which is typically under 850 Hz.See e.g., Gott, G. F., Dutta, S. and Doany, P., “HF Interference withapplication to digital communications”, IEE Proceedings, Vol. 130, Pt.F, No. 5, August 1983. As such, this scheme may reduce or minimize theprobability of burst errors at the input to the convolutional decodercaused by either interference or fading, which is desirable, as aconvolutional decoder is vulnerable to burst errors.

Spectrum Usability Mask (SUM) Generation, Use and Distribution

The fine spectrum occupancy of the HF band, measured in a 110 Hzbandwidth, may be determined at the location of each node by spectrumanalysis. In some embodiments, this may be performed by computing thediscrete Fourier transform (DFT) or Fast Fourier Transform (FFT) which,further, may be incorporated as a part of an OFDM demodulator (e.g.,OFDM demodulator 708 illustrated in FIG. 7 ). It may then be quantizedinto a limited number of quantum levels, such as the following: below-125 dBm, between -125 and -115 dBm, between -115 and -105 dBm, andabove -105 dBm. The quantum levels may be identified by a data wordfitting the number of quantum levels -- in the above example, the fourquantum levels may require a 2-bit word. Other numbers of quantum levelscould be used in the various embodiments.

The communication protocol used in the preferred embodiment may includeperiods of radio silence that are synchronized among all nodes of thenetwork. In some embodiments, the synchronization may be achieved by GPStime. In alternate embodiments, the system time may be distributed amongthe nodes of the network by a master node broadcasting a timingreference signal to all nodes. In military applications, GPS-based timesynchronization has the advantage of reducing the interceptionprobability of the network.

During radio silence, each receiver may measure the fine spectrumoccupancy over a predetermined averaging period. Based on availablespectrum occupancy statistics, a suitable averaging scheme may includethe following: 1 s averaging, performed every 30 s, and the averagedsamples further averaged over a 5-minute sliding time window. HF finespectrum occupancy may be highly correlated over well in excess of5-minute periods.

In the preferred embodiment illustrated in FIGS. 2 and 3, 364 paralleltones, or subcarriers, are shown, occupying a total bandwidth of 40,040Hz. Out of these 364 subcarriers, two sets of 13 subcarriers (batch 1and batch 2), shown shaded in FIG. 4 , may be dedicated to broadcastingthe receiver’s SUM data -they make up the SUM channels. The two batchesof SUM channels may be transmitted in alternating interleaving blocktransmissions and offset with respect to each other by 1540 Hz. Thepurpose of the offset is to introduce additional frequency diversity toimprove avoidance of narrowband interference. It should be noted thatthe SUM channels may have low capacity. As shown below in Table 1, 1.5 smay be required to send the entire SUM data from one interleaving block,during which period, symbols from 113 interleaving blocks may betransmitted. This low SUM channel capacity (975 bps) is acceptablebecause fine spectrum occupancy changes very slowly, and therefore doesnot require rapid sampling.

When in an idle mode, each node may have a reserved, radio silence time,synchronized to GPS disciplined Universal Time, during which it collectsSUM data. No node may transmit during this time. How the SUM data isdistributed to the other nodes depends on whether the radio node is inidle, unicast or broadcast mode. In the unicast mode, the SUM data maybe sent on the designated SUM channels, embedded among traffic carryingsubchannels, as shown in FIG. 4 . Some subchannels, whether carrying SUMdata or traffic, may be suppressed at the transmitter and/or erased atthe receiver, as shown in FIG. 5 . In the broadcast mode, all SUMsubchannels may be transmitted. This is because the fine spectrumoccupancy of some receivers (at ranges in excess of approximately 300km) may not be known to the transmitter.

The schedule for sending SUM data, relative to the transmission time ofthe interleaving block, may be unaffected by the transmission mode(idle, unicast or broadcast), except for suppression/erasure of the SUMdata subchannels when the subchannels coincide with narrowbandinterference at the receiver. The SUM data may be sent on 13 parallelchannels, each bursting at 75 symbols/s. In the preferred embodiment,the SUM data of the entire 40 kHz (approximately) channel may betransmitted every 15 minutes.

Table 1 shows that, according to the transmission time plan describedabove, the entire SUM data for a 40 kHz channel may be sent with arandom linear fountain code in approximately 4.5 s, including 3 repeats.A few more repeats may be required, depending on the congestion in thechannel but only a small fraction of the 15-minute SUM data repetitiontime is consumed.

Table 1 SUM data transmission time-plan Raw SUM bits per SC 2 Hadmardcoded SUM bits per SC 4 No. of SCs whose SUM data is reported in 1 SUMPacket (contents of 2 columns) 28 No. of SCs dedicated to SUM datatransmission in one IL Block (no. of columns) 13 Payload of 1 SUM Packetwith 1 CRC bit added 113 bits Total SUM data in 48 kHz bw channel 1469bits Capacity available for SUM data transmission 975 bps Time reqd. totransmit SUM data once 1.506666667 s Time reqd to transmit IL Block0.013333333 s No. IL Block transmissions required to send all SUM dataonce 113

Applications of Random Linear Fountain Code

Random linear codes may be used in the preferred embodiment for theexchange of SUM data between nodes, and for the transport of usertraffic in the broadcast mode.

Use of Random Linear Fountain Code for Exchanging SUM Data

A random linear fountain code may be used in the preferred embodiment todistribute SUM data among the nodes of the E-WBHF network. Other typesof fountain codes are known in art, any or all of which may be used inthe various embodiments.

The SUM data receivers (e.g., 626 and 628) for own-node and other-noderespectively, and the SUM database 630, may also be included in thereceiver block diagrams (e.g., FIG. 7 , etc.) as they include receivefunctions.

With reference to FIG. 10 , a ‘packet’ may be defined as SUM data bitscarried by 28 subcarriers with adjacent IDs, i.e. subcarriers comprisingthe contents of two adjacent columns of the interleaving block.Specifically, these groupings may include the columns with the followingIDs: (1,2), (3,4), (5,6), (7,8), ... (25, 26). A KxN generator matrix,[G], may be defined in which each column of [G] is a random sequence ofbits - the sequences may be linearly independent between the columns. Itis not required that the columns of [G] be orthogonal - being linearlyindependent suffices.

With reference to FIG. 10 , an encoder may form an inner product betweenthe vectors represented by the columns of [G], i.e. [G_(n]) n = 1 to N,and the packets of the interleaving block, [s_(k]), k = 1 to K (numberof packets in the data file sought to be transported). Here, n is theindex of the encoded packet, t_(n), and k is the index of the sourcepacket which, in the preferred embodiment, may range from 1 to 13.According to the theory of linear random fountain codes, for highlyreliably transport, N needs to exceed K by a modest amount.

The inner product may be calculated by executing the following equation:

t_(n) = Σ[S_(k)]^(T).[G_(kn)]

where the summation is performed over k = 1 to K. Note that t_(n) is notone data bit but an entire packet of data bits. For example, whentransmitting SUM data, the packet contains 113 bits. The process isexplained further, as follows.

Referring to FIG. 9 , the first column of [G_(kn]), i.e. [G_(k1)] isgiven by [G_(k1)] = [1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0]^(T)

The vector, [s_(k]), is depicted below, for different values of k.

$\begin{array}{l}{\left\lbrack \text{S}_{1} \right\rbrack = \left\lbrack {\left\lbrack {\text{SC} - 1_{\text{SUM data}}} \right\rbrack,\left\lbrack {\text{SC} - 2_{\text{SUM data}}} \right\rbrack,\ldots\left\lbrack {\text{SC} - 28_{\text{SUM data}}} \right\rbrack,\left\lbrack \text{CRC} \right\rbrack} \right\rbrack^{\text{T}}\left( 1^{\text{st}} \right.} \\{\text{SUM source data packet})}\end{array}$

$\begin{array}{l}{\left\lbrack \text{S}_{2} \right\rbrack = \left\lbrack {\left\lbrack {\text{SC} - 29_{\text{SUM data}}} \right\rbrack,\left\lbrack {\text{SC} - 30_{\text{SUM data}}} \right\rbrack,\ldots\left\lbrack {\text{SC} - 56_{\text{SUM data}}} \right\rbrack,\left\lbrack \text{CRC} \right\rbrack} \right\rbrack^{\text{T}}(2^{\text{nd}}} \\{\text{Sum source data packet})}\end{array}$

$\begin{array}{l}{\left\lbrack \text{S}_{13} \right\rbrack = \left\lbrack \begin{array}{l}{\left\lbrack {\text{SC} - 337_{\text{SUM data}}} \right\rbrack,\left\lbrack {\text{SC} - 338_{\text{SUM data}}} \right\rbrack,} \\{\ldots\left\lbrack {\text{SC} - 364_{\text{SUM data}}} \right\rbrack,\left\lbrack \text{CRC} \right\rbrack}\end{array} \right\rbrack^{\text{T}}} \\\left( {13^{\text{th}}\text{source SUM data packet}} \right)\end{array}$

Each [SC-i_(SUM) _(data)] may be a 4-bit word representing the Hadamardcoded SUM data for the i-th subcarrier, and [CRC] may represent asingle-bit, cyclic redundancy check sum. As shown in Table-1, thedimension of [si] is (28x4+1=113) bits. Each 113-bit word may representone source SUM-data-packet, representing the SUM data of two adjacentcolumns of the interleaving block, there being 13 such packets in theinterleaving block, plus 1 CRC bit. In the fountain coding scheme, each113 bit packet may be ‘atomic’ - it is received error free or erased. Anerasure may be declared in instances in which the CRC check fails or thelocation of a SUM channel is known to have interference above apredetermined threshold. For example, SUM channels s₄, s₅, s₇ would beerased among the batch 1 channels, and s₁, s₄ would be erased among thebatch 2 channels. Executing equation (1) may replace each sourceSUM-data-packet in the interleaving block with an encodedSUM-data-packet. For example,

t₁ = [S₁] + [S₂] + [S₅] + [S₈] + [S₉] + [S₁₁] + [S₁₂](1^(st)encoded SUM data packet)

$\begin{array}{l}{\text{t}_{\text{2}}\,\text{=}\,\left\lbrack \text{s}_{\text{1}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{2}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{4}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{5}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{6}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{9}} \right\rbrack\,\,\text{+}\,\,\left\lbrack \text{s}_{\text{13}} \right\rbrack\,\,\,\,\,\,} \\{\,\left( {\text{2}^{\text{nd}}\,\text{encoded}\,\,\text{SUM}\,\text{data}\,\text{packet}} \right)}\end{array}$

$\begin{array}{l}{\text{t}_{\text{n}}\text{=}\Sigma\left\lbrack \text{s}_{\text{i}} \right\rbrack\text{,}\,\text{where i is determined}\,\text{by}\,\text{the}\,\text{n-th}\,\text{column}\,\text{of}\,\left\lbrack \text{G}_{\text{kn}} \right\rbrack\,\,\,\,\,\,\,} \\{\text{(n-th}\,\text{encoded}\,\,\text{SUM}\,\text{data}\,\text{packet)}}\end{array}$

Note that n may grow indefinitely beyond K. In the above set ofequations, “+” represents bitwise modulo-2 summation.

The encoded packets, t_(n), may form the output interleaving block 1008and may be transmitted over the air, following the same rules forsubcarrier frequency allocation as in the input interleaving block 1002.All encoded packets may be generated from the same K packets of thesource data file. In the present embodiment for SUM data exchange, K hasa value of 13. As explained further below, it is expected that receiptof approximately (13+14=27) error free packets, regardless of whichpacket is received, is sufficient to ensure error free receipt of theentire file. FIG. 11 shows a Fountain code decoder that complements theencoder shown in FIG. 10 and performs the inverse operation.

FIG. 12 illustrates a method 1200 of processing packets in accordancewith some embodiments. Method 1200 may be performed by a receiver deviceor node, which may be a transceiver device that includes an E-WBHFtransmitter, receiver, and/or transceiver (e.g., E-WBHF transmitter 600illustrated in FIG. 6 , WBHF receiver 700 illustrated in FIG. 7 , etc.).

In block 1202, the receiver device may receive other-node SUM data. Inblock 1204, the receiver device may determine the subcarriers (SCs) thatare to be suppressed and/or the MODCODE for the subcarriers that are tobe utilized. In block 1210, the receiver device may create an inputinterleaving block based on the suppressed subcarriers (from block1204), SUM data to be shared with other nodes (from the own-node SUMdata assessor 1206), and traffic data (from the data sink 1208).

In block 1212, the receiver device may fetch column data from a stored[G] matrix. In block 1214, the receiver device may perform an innerproduct based on decoded data packets S_(k) (from block 1210) and theNth column of the [G] matrix (from block 1212), and generate a fountaincode encoded packet.

In block 1216, the receiver device may populate the output interleavingblock (e.g., output interleaving block 1008 illustrated in FIG. 10 ,etc.) based on the fountain code encoded packet. In block 1218, thereceiver device may provide the output interleaving block as input to amodulator of a transmitter subsystem (e.g., OFDM modulator 614illustrated in FIG. 6 , etc.).

FIG. 13 illustrates a method 1300 of decoding the packets in accordancewith some embodiments. Method 1300 may be performed by a receiver deviceor node, which may be a transceiver device that includes an E-WBHFtransmitter, receiver, or transceiver (e.g., E-WBHF transmitter 600illustrated in FIG. 6 , WBHF receiver 700 illustrated in FIG. 7 , etc.).

In block 1302, the receiver device may receive a data packet fromunoccupied SCs in the interleaving block (IL block). In determinationblock 1304, the receiver device may determine whether the received datapacket passes a cyclic redundancy check (CRC). In response todetermining that the received data packet does not pass the CRC (i.e.,determination block 1304 = “No”), the receiver device may erase the datapacket in block 1306 and receive another data packet in block 1302.Thus, a received packet may be erased in block 1306 at the receiverbased on failing a cyclic redundancy check test on the demodulatedpacket. Or alternatively, responsive to detecting an uncorrected errorin a demodulated data packet, the entire packet is erased from thedemodulated data set in block 1306.

In response to determining that the received data packet passed the CRC(i.e., determination block 1304 = “Yes”), the receiver device may updatea first counter (M) for demodulated packets and update a second counter(N) for error free packets in block 1308. That is, in blocks 1304 and1308, the receiver device may identify packets that are free of errors,keep a first count of the number of packets received, and a second countof the number of packets received error free. In block 1310, thereceiver device may store the receive packet (along with its packet ID,the first and second counters, etc.) in a buffer memory.

In determination block 1312, the receiver device may determine whetherthe value of the second counter (N) exceeds a threshold value(N_(threshold)). In response to determining that the value of the secondcounter (i.e., the count of the number of packets received error free)does not exceed the threshold value (i.e., determination block 1312 =“No”), the receiver device may determine whether the value of the firstcounter (M) exceeds a threshold value (e.g., maximum number of decodingattempts, M_(max), etc.) in determination block 1314. In response todetermining that the value of the first counter (i.e., the count of thenumber of packets received) does not exceed the threshold value (i.e.,determination block 1314 = “No”), the receiver device may commencereceiving another data packet in block 1302. In response to determiningthat the value of the first counter exceeds the threshold value (i.e.,determination block 1314 = “Yes”), the receiver device may generate orindicate an error condition in block 1316.

In response to determining that the value of the second counter (i.e.,the count of the number of packets received error free) exceeds thethreshold value (i.e., determination block 1312 = “Yes”), the receiverdevice may generate a [G] matrix in block 1318. In block 1320, thereceiver device may invert the [G] matrix. In block 1322, the receiverdevice may compute the inner product (e.g., by performing t_(n) =Σ[s_(k]) ^(T).[G_(kn]), etc.). In block 1324, the receiver device maysend the decoded packets (t_(n)) to a data sink (e.g., data sink 728illustrated in FIG. 7 , etc.).

Accurate erasure sensing may be an important aspect of the scheme. Inthe preferred embodiment, this may be based on two independentconditions, any one of which suffices to trigger an erasure (e.g., inblock 1306). First, subcarriers with interference above a threshold aredeemed erased - no attempt is made to demodulate symbols received ondeemed-occupied subcarriers. Second, subcarriers on deemed-unoccupiedsubcarriers are demodulated and the CRC check sum is used to verifyerror free receipt of the packet. Other methods of erasure sensing maybe applicable without deviating from the teachings of this inventiondisclosure.

In block 1310, packets that are received error-free, together with theirpacket IDs, may be stored in an input packet buffer. The packet ID maybe included in the payload of the packet (not incorporated in thepreferred embodiment) or inserted at the receiver based on thesubcarrier’s location in the IL Block. The IL Block ID boundaries(essentially the frame boundaries) may be known from GPS time ordiscoverable via the link management protocol. A count may be kept ofthe number, N, of error free packets received. If N exceeds apredetermined threshold value, N_(threshold), which is expected to besufficient for error-free transport of the entire file as discussedbelow, then the inner product indicated by equation (2) below may becomputed to yield the decoded packets. Note that [G_(nk]) is built withcolumns which correspond to the IDs of the packets received error free.As such, to construct [G_(nk]), it may be necessary to know the IDs ofthe packets comprising [t_(n)].

s_(k)  =  ∑[t_(n)]^(T)  .[G_(nk)]⁻¹

where the summation is performed over n = 1 to N, where N is the numberof received error free packets. N must exceed the number of sourcepackets, K by approximately 14 packets to achieve a confidence greaterthan 0.9999 of recovering the entire file error free.

In some embodiments, to provide a fail-safe exit process, the decodingprocess may be terminated when a certain maximum number of decodingattempts, M_(max), have been completed. In some embodiments, M_(max) maybe fixed by design to ensure that probability of file delivery failurewill be below a target value under a very high percentage of operatingconditions. A large value of M_(max) may increase the file deliverylatency unacceptably. As such, in other embodiments, M_(max) may beself-selected by an intelligent agent in the demodulator based on thelatency tolerance of the mission, which would be known to theintelligent agent. The choice of M_(max) would balance file deliveryfailure probability against the probability of the delivery timeexceeding an objective threshold.

Use of Random Linear Fountain Code for Broadcast of Traffic Data

As mentioned above, in the broadcast mode, fine spectrum occupancy maynot be identical at all receivers. Therefore, the spectrum of thetransmitted waveform generally may not be shaped to optimally avoidinterference at the receiver. An exception to this is short rangebroadcast (e.g., under 300 km, etc.) where there is high likelihood ofcorrelated spectrum occupancy at all receivers. In long range broadcast,spectrum shaping for interference avoidance may not be viable.

Fountain codes may offer an alternate way to make optimal use ofspectrum that is partially blocked by narrowband interference. If someof the packets get through error free, exploiting the spectral gaps inthe band, the entire file may be decoded error free with high confidenceif the number of received error-free packets exceeds a threshold,N_(threshold), where N_(threshold) marginally exceeds the number ofpackets in the file.

In the case of traffic broadcast transmission, the encoding and decodingmethods and implementation structures may remain the same as describedabove for SUM data distribution -- the block diagrams of FIGS. 11 and 12apply equally. However, the payloads (or sizes) of the packets may getbigger as user traffic creates more load. A modulation index up to 8(256 QAM) with ⅚ punctured convolutional coding may be used. This mayneed at least 8+1=9 bits on average. Adding a CRC bit to enable erasuredetection, makes the maximum size of the subcarrier payload to be 9+1=10bits. This is 10/4=2.5 times the size of the payload when transmittingSUM data (113 bits as shown in Table 1). To improve or maximize thepotential of getting individual subcarriers through a congested band,some embodiments may make the packet the same as the subcarrier payload.However, to reduce or minimize the computational load, which may beproportional to the number of packets set per second, it is desirable toincrease the packet size, which reduces the probability of error freetransmission of the whole packet, and therefore allows for more packettransmissions. Specific embodiments may opt for different tradeoffsbetween packet size and implementation complexity.

Detailed Description of Transceiver Transmitter Block Diagram

As mentioned above, FIG. 6 shows a system block diagram of the E-WBHFtransmitter 600. This block diagram applies in all operational modes ofthe network -- (i) SUM data exchange, (ii) unicast traffic transmission,and (iii) broadcast traffic transmission.

Data to be transmitted is available from a data source 602, formatted asfiles containing a finite, known number of packets, K. In the preferredembodiment, K may be 13 for SUM data and application dependent fortraffic transmission (but known at the receiver). Depending on whetherthe traffic transmission is unicast or broadcast, different encoders maybe used to encode the data. These encoders are traffic convolutionalencoder 604 and traffic fountain encoder 606.

The encoded traffic data may be formatted by a bit-to-serial mapper 608,which may populate the transmit block interleaver 610, where theprocedure for placing the traffic or SUM data words, corresponding toQAM symbols, in the cells of the transmit block interleaver 610 isdescribed. The SUM data corresponding to the receiving node may befetched from the SUM database 630 and placed in the appropriate cells ofthe transmit block interleaver 610. Some of the subcarriers in thetransmit block interleaver 610 may be suppressed, also referred to aserased, based on the transmission mode (e.g., SUM data, unicast orbroadcast). Unerased contents of the transmit block interleaver 610 maybe read out to a serial to parallel mapper (SPM) 612 and then applied tomodulate the tones of an OFDM modulator 614. As explained previously, inother embodiments, the modulator may be a non-orthogonal FDM modulator.

In some embodiments, the OFDM modulation may be performed by computingan Inverse Discrete Fourier Transform (IDFT) of the contents of thetransmit block interleaver 610, read out by rows. The transmit waveformafter OFDM modulation may be at an arbitrary baseband frequency of IF,such as complex digital (I/Q), or analog IF, depending on the specificarchitecture of the embodiment.

The output the OFDM modulator transmit waveform may be upconverted tothe desired frequency, or frequencies, in the HF band and transmittedthrough the antenna coupler 618 and the antenna 620. In embodiments inwhich carrier aggregation is used, the transmission may be at aplurality of non-contiguous frequencies in parallel. In the latter case,a multichannel, parallel, upconverter is required.

Some functions of the transmitter may be influenced by certain receivedparameters. Functional blocks involved in the reception and processingof these parameters are described below. Data symbols received throughthe receive subsystem 622 may be collected in the receive blockinterleaver 624. During periods of radio silence, the received symbolsmay be spectrum analyzed to generate the SUM data for the entireoperating band, which is 40.04 kHz in the preferred embodiment withoutcarrier aggregation but may be less when carrier aggregation is used.The generation of SUM data during radio silence, and their encoding by afountain code may be performed in the own-node SUM datagenerator/fountain-encoder 628.

During periods of non-radio-silence, SUM data sent by other nodes may becollected from the receive block interleaver 624 and demodulated anddecoded (using a Fountain Decoder) in block 626.

The SUM data from blocks 626 and 628, representing the SUM data receivedfrom other nodes and own node, may be deposited in the SUM database 630,together with the packet IDs identifying each packet. Every node mayinclude a copy of the SUM database 630, which may be continuallysynchronized through the process of SUM data exchange every 15 minuteswhen the node is active (ready for transmit or receive).

During unicast or short range broadcast, the SUM data to be transmittedmay be fetched from the local SUM database 630. The SUM database 630 mayalso provide the IDs of the suppressed carriers fed to the transmitblock interleaver 610. During long range broadcast transmission, nosubcarriers are suppressed. During short range broadcast, the suppressedcarrier IDs may be based on own-node SUM data.

Receiver Block Diagram

With reference to FIG. 7 , signals received in a 48 kHz segment of theHF band, which may be contiguous or non-contiguous, may be receivedthough an antenna 702 and antenna coupler 704 and fed to a receiver (Rx)706, which may downconvert the signal to complex baseband or IF forsignal processing. In embodiments in which carrier aggregation is used,the downconversion may involve a plurality of parallel downconverters.

The signal may be fed to an OFDM (or FDM) demodulator 708. The OFDMdemodulation may be implemented by a Discrete Fourier Transform (DFT),which may recover the complex baseband symbols representing themodulation envelopes of the 364 subcarriers in the present embodiment.The envelopes may be read into the receive block interleaver (RBI) 720by rows, and read out by columns to a symbol-to-bit-mapper (SBM) 722.The latter may be QAM (including BPSK, QPSK) demodulator that feeds atraffic convolutional decoder 724 in the unicast mode and a trafficfountain decoder 726 in the broadcast mode.

The various embodiments advance the state of the art of wideband HFcommunication beyond the current art, represented by the WBHF standard,in at least the following major aspects. These aspects do not limit, inany way, the draft claims which relate to additional innovations.

In a first set of embodiments, in a mesh network comprising a pluralityof transmitting and receiving nodes in a congested band, the networksenses the interference spectrum occupancies at a plurality of receivernodes and synthesizes transmit waveforms at the transmit nodes so thatthe spectra of the transmit waveforms fit into the gaps of theinterference spectra at the receiver nodes. Further, the transmitwaveforms may utilize a substantial part of the unoccupied spectrum atthe receiver, to maximize the spectral efficiency of the waveform whilealso minimizing exposure to the interference spectrum.

The methods of radio communications may also include assessing theinterference spectrum occupancy with a measurement bandwidth ofapproximately 110 Hz, referred to as fine spectrum occupancy. The totalspectrum occupancy of the transmitted signal may be substantiallygreater than 3 kHz.

The methods of radio communications may result in a substantialreduction in the transmit power compared to a system that does not adaptto the fine interference spectral occupancy.

The methods of radio communications, such as designing the transmitsignal spectrum to complement the receiver’s interference spectraldensity, may be applied to radiofrequency bands in general and are notlimited to HF. Here “complement” means that the sum of the desiredsignal and interference signal spectra at the receiver are substantiallyconstant).

The band of application in the preferred embodiment is HF, with achannel bandwidth that is substantially greater than the nominalbandwidth of 3 kHz standardized by ITU for a single voice circuit.

The transmit waveform may be synthesized by excising subbands from acomposite wideband signal, e.g. 48 kHz bandwidth in the preferredembodiment. The composite wideband signal may include a plurality ofstandard, 3 KHz voice channels that may be contiguous in someembodiments and discontiguous in alternate embodiments.

In some embodiments, the subband excision may be performed at thetransmitter by suppressing subcarriers in an OFDM signal. Alternatemethods of narrowband frequency excision may be used, such as excludingindividual filters in a non-OFDM filter bank, or inserting bandstop, ornotch, filters in a wideband signal.

Spectrum occupancy information may be exchanged among the nodes of thenetwork by quantizing and compressing the information into a SpectrumUsability Mask parameter - SUM data -- which may be shared among thenodes.

SUM data may be shared using a protocol that does not require priorknowledge of the spectrum occupancy at the receiver. A fountain code maybe used for sharing SUM data, which may ensure a very high probabilityof delivery of a data block through a channel with random erasures. TheSUM data sharing protocol may leverage the time-stationarity of HFspectrum occupancy.

In some cases of the first embodiment, the spectrum occupancy may beknown to be reciprocal between the transmitter and the receiver (e.g.when the separation distance between the transmitting and receivingnodes are less than 300 km, etc.). This information may be leveraged byobviating the need for sharing SUM data.

A second set of embodiments may include broadcast applications. The sameinformation may be received by a plurality of nodes with unlikeinterference spectrum occupancies at their respective locations. Inthese embodiments, the transmit waveform may occupy the entire widebandchannel but interference avoidance may be achieved at the receiver byexcising subbands matched to the interference spectrum occupancy.

The spectrum excision may be performed by erasing OFDM subcarriers, inembodiments in which OFDM was the waveform used by the transmitter.Other methods of spectrum excision, such as an interference whiteningfilter, may also be used.

Some embodiments may include methods of communicating through a wirelesscommunication network, using a radio channel and a plurality oftransmitters and receivers, in which the band that is occupied by thechannel is also partially occupied by narrowband interference, and atransmitter communicates with the receiver using a waveform whosespectrum occupancy adaptively avoids the spectrum occupancy of theinterference at the receiver.

In some embodiments, the narrowband interference has a bandwidth that istypically less than 110 Hz. In some embodiments, the medium ofcommunication is the HF band. In some embodiments, the use of the methodresults in a substantial reduction of transmit power or increasedthroughput compared to a system that does not so adapt to the spectrumoccupancy of the interference at the receiver. In some embodiments, thereceiver senses the spectrum occupancy of the received interferenceduring a period of radio silence of the network and communicates to thetransmitter a plurality of attributes of the spectrum occupancy of theinterference described by a spectrum usability mask.

In some embodiments, the spectrum occupancy of the received interferenceis determined by computing a discrete Fourier Transform of the receivedsignal. In some embodiments, the spectrum occupancy of the receivedinterference is determined by computing a Fast Fourier Transform of thereceived signal.

In some embodiments, a transmitter that is within a threshold separationdistance from the receiver, such as approximately 300 km, senses thespectrum occupancy of the received interference and uses the saidspectrum occupancy to shape the spectrum of signals transmitted by it.Research has shown that, in the HF band, interference spectral occupancyis usually similar at such separations. See e.g., S. Dutta and Gott,G.F., “Correlation of HF interference spectra with range”, IEEProceedings, Vol. 128, Pt. F, No. 4, August 1981. In some embodiments,the spectrum usability mask identifies a threshold level of interferencepower received by a known subcarrier that is not exceeded when averagedover a known period of time. In some embodiments, the spectrum usabilitymask identifies upper and lower threshold limits of interference powerreceived by a known subcarrier such that, when the interference power isaveraged over a known period of time, the value of the averageinterference power is bounded by the upper and lower threshold limits.

Some embodiments may include methods of communicating with a transmitterand receiver, using a frequency division multiplexed waveform thatincludes a plurality of subcarriers, in which some of the subcarriersare suppressed from transmission based on the spectrum usability mask atthe receiver. In some embodiments, the power saved by suppressingsubcarriers may be applied towards transmitting subcarriers that havenot been suppressed.

Some embodiments may include methods of communicating with a transmitterand receiver, using a frequency division multiplexed waveform thatincludes a plurality of subcarriers, in which the choice of modulationand coding used for each transmitted subcarrier is based on theinterference power within the spectrum occupied by the subcarrier at thereceiver. In some embodiments, the plurality of subcarriers forms anorthogonal, frequency division multiplexed waveform.

Some embodiments may include methods of receiving a frequency divisionmultiplexed signal, including a plurality of subcarriers carryingmodulated data which is demodulated by the receiver into a demodulateddata set, in which responsive to determining that some of thesubcarriers contain cochannel interference whose power is above athreshold value, the demodulated data carried by the subcarrierscontaining cochannel interference are erased from the demodulated dataset.

Some embodiments may include methods of receiving a frequency divisionmultiplexed signal, including a plurality of subcarriers carryingmodulated data which is demodulated by the receiver into a demodulateddata set, in which responsive to detecting an uncorrected error in ademodulated data packet, the entire packet is erased from thedemodulated data set.

Some embodiments may include methods of communicating a file comprisinga finite number of source data packets through a frequency divisionmultiplexed wireless communication channel that is partially occupied bynarrowband interference by using a fountain code to encode the sourcedata packets, transmitting the encoded data packets using allsubcarriers, regardless of whether they are encountering interference atthe receiver, at the receiver -identifying packets that are free oferrors, keeping a first count of the number of packets received, and asecond count of the number of packets received error free, andcontinuing to transmit encoded packets until the second count exceeds athreshold, responsive to which the file of transmitted data is decoded.

In some embodiments, the method may include abandoning decoding attemptsfor the file in instances in which the first count exceeds a maximumvalue. In some embodiments, a received packet may be erased at thereceiver based on knowledge of the interference spectrum occupancy atthe receiver. In some embodiments, a received packet may be erased atthe receiver based on failing a cyclic redundancy check test on thedemodulated packet. In some embodiments, the wireless communicationchannel includes a single contiguous channel in the radio spectrum.

In some embodiments, the wireless communication channel includes aplurality of discontiguous subchannels in the radio spectrum, thesubchannels being of arbitrary bandwidths, and which are aggregated inthe receiver to form a contiguous channel at an intermediate frequency.In some embodiments, the intermediate frequency may be zero (0) Hz andthe signals may be represented in complex baseband form.

As discussed in detail below, non-contiguous carrier aggregation offersthe advantage of pre-selecting less congested, 3 kHz bandwidth,‘standard channels’ to synthesize the objective waveform. Assume thatout of 16, only 8 standard channels are selected as having usablespectra. In this example, the receiver may indicate the SUM data forthese 8 discontiguous, standard channels, including the ID of each ofthe selected standard channels. On receiving the SUM data fordiscontiguous channels, the transmitter may synthesize 24 kHz (not 48kHz) transmission channel, comprising an aggregate of 8 standardchannels. A node may process this 24 kHz channel for spectrum excisionaccording to the received SUM data, and then transmit each standardchannel at its appropriate frequency in the HF band, which will not becontiguous relative to the other standard channels. The processing ofthe 24 kHz channel by the transmitter will occur at zero (0) Hz IF, withcomplex baseband signal representation, which is preferred for a DSPimplementation. The receiver will receive the 8 standard channels fromtheir specific, discontiguous frequencies in the HF band and translatethem to zero (0) Hz IF, with complex baseband signal representation.That is, the signals may be represented in complex baseband form. Atthat zero (0) Hz IF, the signals will occupy a band of -12 kHz to +12kHz, as they did at the transmitter. Thus, from an end-to-endperspective, it will seem as if the channel was 24 kHz wide, although itincludes standard channels distributed over 48 kHz in the HF band.

FIG. 14 illustrates a method 1400 of communicating data packets througha wireless communication network in accordance with some embodiments.Method 1400 may be performed by a first node 1450 and/or a second node1452, any of all of which may be a transceiver device that include anE-WBHF transmitter, receiver, or transceiver (e.g., E-WBHF transmitter600 illustrated in FIG. 6 , WBHF receiver 700 illustrated in FIG. 7 ,etc.).

In block 1402, the first node 1450 may determine spectrum occupancyattributes of narrowband interference on a communication channel at thelocation of the first node 1450 (i.e., at its current location). In someembodiments, determining the spectrum occupancy attributes in block 1402may include the first node 1450 sensing the power spectral density ofthe narrowband interference during a period of radio silence, andgenerating a spectrum usability mask from the sensed power spectraldensity. In some embodiments, determining the spectrum occupancyattributes in block 1402 may include the first node 1450 computing apower spectral density of the waveform based on a discrete Fouriertransform (or based on a fast Fourier transform, etc.), and generating aspectrum usability mask by quantizing the power spectral densityrelative to a set of threshold values. In some embodiments, generatingthe spectrum usability mask in block 1402 may include the first node1450 identifying a threshold level of interference power received by aknown subcarrier that is not exceeded when averaged over a known periodof time. In some embodiments, generating the spectrum usability mask inblock 1402 may include the first node 1450 identifying upper and lowerthreshold limits of interference power received by a known subcarriersuch that, when the interference power is averaged over a known periodof time, the value of the average interference power is bounded by theupper and lower threshold limits. In block 1404, the first node 1450 maybroadcast the determined spectrum occupancy attributes for reception byone or more other nodes.

In block 1406, the second node 1452 may receive a broadcast thatincludes spectrum occupancy attributes of narrowband interference on acommunication channel at the location of first node 1450.

In block 1408, the second node 1452 may generate or spectrally shape awaveform (e.g., multicarrier OFDM waveform illustrated in FIG. 1 , etc.)based on the spectrum occupancy attributes of the narrowbandinterference on the communication channel at the location of the firstnode 1450, and transmit a data packet to the first node 1450 using thewaveform generated based on the spectrum occupancy attributes of thenarrowband interference on the communication channel at the location ofthe first node 1450.

In some embodiments, transmitting the data packet in block 1408 mayinclude the second node 1452 using a frequency division multiplexedwaveform that includes a plurality of subcarriers (e.g., a plurality ofmutually orthogonal subcarriers, each subcarrier being modulated with asubset of the data contained in one transmit interleaving block.), andsuppressing at least some of the subcarriers from transmission based onthe spectrum occupancy attributes of the narrowband interference on thecommunication channel. In some embodiments, the second node 1452 may beconfigured to apply the power that is saved by suppressing thesubcarriers towards transmitting the subcarriers that have not beensuppressed.

In some embodiments, transmitting the data packet in block 1408 mayinclude the second node 1452 selecting a modulation and coding schemefor each transmitted subcarrier based on an interference power withinspectrum occupied by the subcarrier at the first node 1450.

In block 1410, the first node 1450 may receive the data packets via thewaveform generated based on the spectrum occupancy attributes of thenarrowband interference on the communication channel at the location offirst node 1450.

In some embodiments, such as long range broadcast data communications,the spectrum occupancy attributes may be dissimilar at the plurality ofreceiving first nodes 1450. In this case, second node 1452 may transmiton all subcarriers, regardless of the spectrum occupancy attributes atthe locations of first nodes 1450. In this broadcast case, the firstnodes 1450 may generate a demodulated data set by demodulating modulateddata carried by subcarriers in the waveform, and erase the data carriedby the subcarriers of the waveform that include cochannel interference.

In some broadcast embodiments as described above, the first nodes 1450may generate a demodulated data set by demodulating modulated datacarried by subcarriers in the waveform, determine whether thedemodulated data set includes a demodulated data packet that includes anuncorrected error, and erase the demodulated data packet in response todetermining that the demodulated data set includes the demodulated datapacket that includes the uncorrected error.

In some broadcast embodiments as described above, the first nodes 1450may identify packets that are free of errors, maintain a first count ofthe number of packets received in the receiver device, and maintain asecond count of the number of packets received error free in thereceiver device.

FIG. 15 illustrates a method 1500 of communicating a file that includesa finite number of source data packets through a frequency divisionmultiplexed wireless communication channel that is partially occupied bynarrowband interference in accordance with some embodiments. Method 1500may be performed by a plurality of first nodes 1550 and/or a second node1552, any or all of which may be a transceiver device that includes anE-WBHF transmitter, receiver, or transceiver (e.g., E-WBHF transmitter600 illustrated in FIG. 6 , WBHF receiver 700 illustrated in FIG. 7 ,etc.).

In some embodiments, the file (and source data packets) may includeinformation about the spectral occupancy of interference received by thesecond node 1552, and the second node 1552 may broadcast the spectraloccupancy information for reception by the plurality of first nodes1550. In some embodiments, the file (and source data packets) mayinclude user data, and the second node 1552 may broadcast the file forreception by a plurality of plurality of first nodes 1550 havingdissimilar interference spectral occupancies at their respectivelocations.

With reference to FIG. 15 , in block 1502, the second node 1552 may usea fountain code to encode the source data packets of the file. Asdiscussed above, fountain codes may make optimal use of spectrum that ispartially blocked by narrowband interference. If some of the packets getthrough error free, exploiting the spectral gaps in the band, the entirefile may be decoded error free with high confidence if the number ofreceived error-free packets exceeds a threshold, N_(threshold), whereN_(threshold) marginally exceeds the number of packets in the file. Assuch, a fountain code may be used in block 1502 to, for example, sharespectrum usability mask (SUM) data with other nodes in the networkand/or to assure, with very high confidence, that all nodes have errorfree copies of the SUM data of every node of the network. The fountaincode may also be used for long-range broadcast traffic, where thereceivers are at a distance greater than a minimum limit, such as 300km, beyond which range the interference spectrum occupancy is typicallyuncorrelated.

In block 1504, the second node 1552 may commence transmitting theencoded data packets of the file to one or more of the plurality offirst nodes 1550, using all subcarriers regardless of whether they areencountering interference at the receiver (first nodes 1550). The secondnode 1552 may continue to transmit the encoded packets until either anacknowledgment of file delivery message is received in block 1520 or afailure of file delivery message is received in block 1522 from athreshold number of first nodes 1550.

In block 1506, a first node 1550 may commence receiving encoded datapackets. For example, as discussed above with reference to block 1302 ofFIG. 13 , the first node 1550 may receive a data packet from unoccupiedSCs in the interleaving block (IL block) in block 1506.

In block 1508, the first node 1550 may identify the received packetsthat are free of errors. For example, as discussed above with referenceto block 1304 of FIG. 13 , the first node 1550 may determine whether thereceived data packet passes a cyclic redundancy check (CRC) in block1508. As discussed above with reference to block 1306 of FIG. 13 , insome embodiments, the first node 1550 may be further configured to eraseone or more demodulated packets in response to determining that thedemodulated packet failed the CRC test. In some embodiments, the firstnode 1550 may be configured to erase one or more received packets basedon spectrum occupancy attributes of narrowband interference on thecommunication channel at the location of the second node 1552.

In block 1510, the first node 1550 may keep a first count of the numberof received packets. In block 1512, the first node 1550 may keep asecond count of the number of the received packets that are free oferrors. For example, as discussed above with reference to block 1308 ofFIG. 13 , the first node 1550 may update a first counter (M) fordemodulated packets and update a second counter (N) for error freepackets in blocks 1510 and 1512.

In determination block 1514, the first node 1550 may determine whetherthe second count exceeds a threshold. For example, as discussed abovewith reference to block 1312 of FIG. 13 , the first node 1550 maydetermine whether the value of a second counter (N) exceeds a thresholdvalue (N_(threshold)) in block 1514.

In response to determining that the second count exceeds a threshold(i.e., determination block 1514 = “Yes”), the first node 1550 may decodethe file of transmitted encoded data packets in block 1516. For example,as discussed above with reference to blocks 1318-1324 of FIG. 13 , thefirst node 1550 may generate a [G] matrix, invert the [G] matrix,compute the inner product (e.g., by performing t_(n) =Σ[s_(k)]^(T).[G_(kn)]⁻¹, etc.), and send the decoded packets (t_(n)) toa data sink (e.g., data sink 728 illustrated in FIG. 7 , etc.) in block1516. In addition, the first node 1550 may send a notice ofacknowledgment of file delivery to the second node 1552 in block 1516.

In response to determining that the second count does not exceed thethreshold (i.e., determination block 1514 = “No”), the first node 1550may determine whether the first count exceeds a threshold indetermination block 1518. For example, as discussed above with referenceto block 1314 of FIG. 13 , the first node 1550 may determine whether thevalue of the first counter (M) exceeds a threshold value (e.g., maximumnumber of decoding attempts, M_(max), etc.) in determination block 1518.

In response to determining that the first count does not exceed thethreshold (i.e., determination block 1518 = “No”), the first node 1550may continue to receive and count the data packets by repeating theoperations in blocks 1506-1516. In response to determining that thefirst count exceeds the threshold (i.e., determination block 1518 =“Yes”), the first node 1550 may abandon any decoding attempts for thefile and send a notice of failure of file delivery to the second node1552 to indicate an error condition.

The various embodiments may be implemented on a number of multicore andmultiprocessor systems, including a system-on-chip (SOC). An SOC may bea single integrated circuit (IC) chip that contains multiple resourcesor independent processors integrated on a single substrate. A single SoCmay contain circuitry for digital, analog, mixed-signal, andradio-frequency functions. A single SoC also may include any number ofgeneral purpose or specialized processors (e.g., network processors,digital signal processors, modem processors, video processors, etc.),memory blocks (e.g., ROM, RAM, Flash, etc.), and resources (e.g.,timers, voltage regulators, oscillators, etc.). For example, an SoC mayinclude an applications processor that operates as the SoC’s mainprocessor, central processing unit (CPU), microprocessor unit (MPU),arithmetic logic unit (ALU), etc. SoCs also may include software forcontrolling the integrated resources and processors, as well as forcontrolling peripheral devices. A multicore processor may be a singleintegrated circuit (IC) chip or chip package that contains two or moreindependent processing cores (e.g., CPU core, modem processor core,etc.) configured to read and execute program instructions. A SoC mayinclude multiple multicore processors, and each processor in an SoC maybe referred to as a core. A multiprocessor may be a system or devicethat includes two or more processing units configured to read andexecute program instructions.

FIG. 16 is an architectural diagram illustrating an examplesystem-on-chip (SOC) 1600 architecture that may be used to implement thevarious aspects. The SOC 1600 may include a number of heterogeneousprocessors, such as a digital signal processor (DSP) 1602, a modemprocessor 1604, a graphics processor 1606, and an application processor1608. The SOC 1600 may also include one or more coprocessors 1610 (e.g.,vector co-processor) connected to one or more of the processors 1602,1604, 1606, 1608. Each processor 1602, 1604, 1606, 1608, 1610 mayinclude one or more cores, and each processor/core may performoperations independent of the other processors/cores. For example, theSOC 1600 may include a processor that executes a first type of operatingsystem (e.g., FreeBSD, LINIX, OS X, etc.) and a processor that executesa second type of operating system (e.g., Microsoft Windows 11, etc.).

The SOC 1600 may also include analog circuitry and custom circuitry 1614for managing sensor data, analog-to-digital conversions, wireless datatransmissions, and for performing other specialized operations, such asprocessing encoded audio signals for games and movies. The SOC 1600 mayfurther include system components and resources 1616, such as voltageregulators, oscillators, phase-locked loops, peripheral bridges, datacontrollers, memory controllers, system controllers, access ports,timers, and other similar components used to support the processors andclients running on a computing device.

The system components 1616 and custom circuitry 1614 may includecircuitry to interface with peripheral devices, such as cameras,electronic displays, wireless communication devices, external memorychips, etc. The processors 1602, 1604, 1606, 1608 may be interconnectedto one or more memory elements 1612, system components and resources1616 and custom circuitry 1614 via an interconnection/bus module 1624,which may include an array of reconfigurable logic gates and/orimplement a bus architecture (e.g., CoreConnect, AMBA, etc.).Communications may be provided by advanced interconnects, such as highperformance networks-on chip (NoCs).

The SOC 1600 may further include an input/output module (notillustrated) for communicating with resources external to the SOC, suchas a clock 1618 and a voltage regulator 1620. Resources external to theSOC (e.g., clock 1618, voltage regulator 1620) may be shared by two ormore of the internal SOC processors/cores (e.g., DSP 1602, modemprocessor 1604, graphics processor 1606, applications processor 1608,etc.).

In addition to the SOC 1600 discussed above, the various aspects may beimplemented in a wide variety of computing systems, which may include asingle processor, multiple processors, multicore processors, or anycombination thereof.

Some embodiments may be implemented on any of a variety of commerciallyavailable server devices, such as the server 1700 illustrated in FIG. 17. Such a server 1700 typically includes a processor 1701 coupled tovolatile memory 1702 and a large capacity nonvolatile memory, such as adisk drive 1703. The server 1700 may also include a floppy disc drive,compact disc (CD) or DVD disc drive 1704 coupled to the processor 1701.The server 1700 may also include network access ports 1705 coupled tothe processor 1701 for establishing data connections with a network1706, such as a local area network coupled to other operator networkcomputers and servers.

The processor 1701 may be any programmable microprocessor, microcomputeror multiple processor chip or chips that can be configured by softwareinstructions (applications) to perform a variety of functions, includingthe functions of the various embodiments described below. Multipleprocessors 1701 may be provided, such as one processor dedicated towireless communication functions and one processor dedicated to runningother applications. Typically, software applications may be stored inthe internal memory before they are accessed and loaded into theprocessor 1701. The processor 1701 may include internal memorysufficient to store the application software instructions.

As used in this application, the terms “component,” “module,” “system,”and the like are intended to include a computer-related entity, such as,but not limited to, hardware, firmware, a combination of hardware andsoftware, software, or software in execution, which are configured toperform particular operations or functions. For example, a component maybe, but is not limited to, a process running on a processor, aprocessor, an object, an executable, a thread of execution, a program,and/or a computer. By way of illustration, both an application runningon a computing device and the computing device may be referred to as acomponent. One or more components may reside within a process and/orthread of execution and a component may be localized on one processor orcore and/or distributed between two or more processors or cores. Inaddition, these components may execute from various non-transitorycomputer readable media having various instructions and/or datastructures stored thereon. Components may communicate by way of localand/or remote processes, function or procedure calls, electronicsignals, data packets, memory read/writes, and other known computer,processor, and/or process related communication methodologies.

Various embodiments illustrated and described are provided merely asexamples to illustrate various features of the claims. However, featuresshown and described with respect to any given embodiment are notnecessarily limited to the associated embodiment and may be used orcombined with other embodiments that are shown and described. Further,the claims are not intended to be limited by any one example embodiment.For example, one or more of the operations of the methods 1200 and 1300may be substituted for or combined with one or more operations of any ofmethods 1200 and 1300.

The processors discussed in this application may be any programmablemicroprocessor, microcomputer or multiple processor chip or chips thatcan be configured by software instructions (applications) to perform avariety of functions, including the functions of the various embodimentsdescribed above. In some devices, multiple processors may be provided,such as one processor dedicated to wireless communication functions andone processor dedicated to running other applications. Typically,software applications may be stored in the internal memory before theyare accessed and loaded into the processors. The processors may includeinternal memory sufficient to store the application softwareinstructions. In many devices, the internal memory may be a volatile ornonvolatile memory, such as flash memory, or a mixture of both. For thepurposes of this description, a general reference to memory refers tomemory accessible by the processors including internal memory orremovable memory plugged into the device and memory within theprocessors themselves. Additionally, as used herein, any reference to amemory may be a reference to a memory storage and the terms may be usedinterchangeable.

The foregoing method descriptions and the process flow diagrams areprovided merely as illustrative examples and are not intended to requireor imply that the steps of the various embodiments must be performed inthe order presented. As will be appreciated by one of skill in the artthe order of steps in the foregoing embodiments may be performed in anyorder. Words such as “thereafter,” “then,” “next,” etc. are not intendedto limit the order of the steps; these words are simply used to guidethe reader through the description of the methods. Further, anyreference to claim elements in the singular, for example, using thearticles “a,” “an” or “the” is not to be construed as limiting theelement to the singular.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The hardware used to implement the various illustrative logics, logicalblocks, modules, components, and circuits described in connection withthe embodiments disclosed herein may be implemented or performed with ageneral purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but, in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Alternatively, some steps or methods may be performed bycircuitry that is specific to a given function.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored as one or moreinstructions or code on a non-transitory computer-readable medium ornon-transitory processor-readable medium. The steps of a method oralgorithm disclosed herein may be embodied in a processor-executablesoftware module and/or processor-executable instructions, which mayreside on a non-transitory computer-readable or non-transitoryprocessor-readable storage medium. Non-transitory server-readable,computer-readable or processor-readable storage media may be any storagemedia that may be accessed by a computer or a processor. By way ofexample but not limitation, such non-transitory server-readable,computer-readable or processor-readable media may include RAM, ROM,EEPROM, FLASH memory, CD-ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any other medium thatmay be used to store desired program code in the form of instructions ordata structures and that may be accessed by a computer. Disk and disc,as used herein, includes compact disc (CD), laser disc, optical disc,DVD, floppy disk, and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofnon-transitory server-readable, computer-readable and processor-readablemedia. Additionally, the operations of a method or algorithm may resideas one or any combination or set of codes and/or instructions on anon-transitory server-readable, processor-readable medium and/orcomputer-readable medium, which may be incorporated into a computerprogram product.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thescope of the invention. Thus, the present invention is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the following claims and the principles andnovel features disclosed herein.

What is claimed is:
 1. A method of communicating data packets through awireless communication network, comprising: receiving, by a transceiverdevice from a receiver device, spectrum occupancy attributes ofnarrowband interference on a communication channel at a location of thereceiver device; and transmitting, from the transceiver device to thereceiver device, a data packet using a waveform generated based on thespectrum occupancy attributes of the narrowband interference on thecommunication channel at the location of the receiver device.
 2. Themethod of claim 1, wherein transmitting the data packet using thewaveform generated based on the spectrum occupancy attributes of thenarrowband interference on the communication channel at the location ofthe receiver device comprises: transmitting the data packet using afrequency division multiplexed waveform comprising a plurality ofsubcarriers and suppressing at least some of the subcarriers fromtransmission based on the spectrum occupancy attributes of thenarrowband interference on the communication channel; and assigning userdata to be carried only by the transmitted subcarriers.
 3. The method ofclaim 2, wherein transmitting the data packet using the frequencydivision multiplexed waveform comprising the plurality of subcarrierscomprises: transmitting the data packet using a frequency divisionmultiplexed waveform that includes a plurality of mutually orthogonalsubcarriers, wherein each of the mutually orthogonal subcarriers ismodulated with a subset of the data contained in one transmitinterleaving block.
 4. The method of claim 2, further comprisingapplying power saved by suppressing the subcarriers towards transmittingthe subcarriers that have not been suppressed.
 5. The method of claim 1,wherein transmitting the data packet using the waveform generated basedon the spectrum occupancy attributes of the narrowband interference onthe communication channel at the location of the receiver devicecomprises: selecting a modulation and coding scheme for each transmittedsubcarrier based on an interference power within spectrum occupied bythe subcarrier at the receiver device.
 6. The method of claim 1, whereintransmitting the data packet using the waveform generated based on thespectrum occupancy attributes of the narrowband interference on thecommunication channel at the location of the receiver device comprises:generating the waveform based on the spectrum occupancy attributes ofthe narrowband interference on the communication channel at the locationof the transceiver device.
 7. The method of claim 1, further comprising:determining, by the transceiver device, spectrum occupancy attributes ofnarrowband interference on the communication channel at the location ofthe transceiver device; and broadcasting, by the transceiver device, thedetermined spectrum occupancy attributes for reception by one or moreother devices.
 8. The method of claim 7, wherein determining thespectrum occupancy attributes of the narrowband interference on thecommunication channel comprises: sensing the power spectral density ofthe narrowband interference during a period of radio silence; andgenerating a spectrum usability mask from the sensed power spectraldensity.
 9. The method of claim 7, wherein determining the spectrumoccupancy attributes of narrowband interference on the communicationchannel at the location of the receiver device comprises: computing apower spectral density of the waveform: based on a discrete Fouriertransform, or based on a fast Fourier transform; and generating aspectrum usability mask by quantizing the power spectral densityrelative to a set of threshold values.
 10. The method of claim 9,wherein generating the spectrum usability mask by quantizing the powerspectral density relative to the set of threshold values comprises:identifying a threshold level of interference power received by a knownsubcarrier that is not exceeded when averaged over a known period oftime.
 11. The method of claim 9, wherein generating the spectrumusability mask by quantizing the power spectral density relative to theset of threshold values comprises: identifying upper and lower thresholdlimits of interference power received by a known subcarrier such that,when the interference power is averaged over a known period of time, avalue of the average interference power is bounded by the upper andlower threshold limits.
 12. The method of claim 7, further comprising:generating a demodulated data set by demodulating modulated data carriedby subcarriers in the waveform; and erasing data carried by thesubcarriers of the waveform that include cochannel interference.
 13. Themethod of claim 7, further comprising: generating a demodulated data setby demodulating modulated data carried by subcarriers in the waveform;determining whether the demodulated data set includes a demodulated datapacket that includes an uncorrected error; and erasing the demodulateddata packet in response to determining that the demodulated data setincludes the demodulated data packet that includes the uncorrectederror.
 14. The method of claim 7, further comprising: identifyingpackets that are free of errors; maintaining a first count of the numberof packets received in the receiver device; and maintaining a secondcount of the number of packets received error free in the receiverdevice.
 15. The method of claim 7, wherein the communication channelcomprises a plurality of discontiguous subchannels in the radiospectrum, the subchannels having arbitrary bandwidths, the methodfurther comprising: aggregating, by a transceiver device, the pluralityof discontiguous subchannels to form a contiguous channel at anintermediate frequency.
 16. The method of claim 7, wherein: theintermediate frequency in the transceiver device is zero Hz; and thesignals are represented in the transceiver device in complex basebandform.
 17. A transceiver device, comprising: a processor configured to:receive, from a receiver device, spectrum occupancy attributes ofnarrowband interference on a communication channel at a location of thereceiver device; and transmit, to the receiver device, a data packetusing a waveform generated based on the spectrum occupancy attributes ofthe narrowband interference on the communication channel at the locationof the receiver device.
 18. The transceiver device of claim 17, whereinthe processor is configured to transmit the data packet using thewaveform generated based on the spectrum occupancy attributes of thenarrowband interference on the communication channel at the location ofthe receiver device by: transmitting the data packet using a frequencydivision multiplexed waveform comprising a plurality of subcarriers andsuppressing at least some of the subcarriers from transmission based onthe spectrum occupancy attributes of the narrowband interference on thecommunication channel; and assigning user data to be carried only by thetransmitted subcarriers.
 19. The transceiver device of claim 18, whereinthe processor is configured to transmit the data packet using thefrequency division multiplexed waveform comprising the plurality ofsubcarriers by: transmitting the data packet using a frequency divisionmultiplexed waveform comprising a plurality of mutually orthogonalsubcarriers, wherein each of the mutually orthogonal subcarriers ismodulated with a subset of the data contained in one transmitinterleaving block.
 20. The transceiver device of claim 18, wherein theprocessor is further configured to apply power saved by suppressing thesubcarriers towards transmitting the subcarriers that have not beensuppressed.
 21. The transceiver device of claim 17, wherein theprocessor is further configured to: select a modulation and codingscheme for each transmitted subcarrier based on an interference powerwithin spectrum occupied by the subcarrier at the receiver device. 22.The transceiver device of claim 17, wherein the processor is furtherconfigured to: generate the waveform based on the spectrum occupancyattributes of the narrowband interference on the communication channelat the location of the transceiver device.
 23. The transceiver device ofclaim 17, wherein the processor is further configured to: determine thespectrum occupancy attributes of narrowband interference on thecommunication channel at the location of the transceiver device; andbroadcast the determined spectrum occupancy attributes for reception byone or more other devices.
 24. The transceiver device of claim 23,wherein the processor is configured to determine the spectrum occupancyattributes of the narrowband interference on the communication channelby performing operations that include: sensing the power spectraldensity of the narrowband interference during a period of radio silence;and generating a spectrum usability mask from the sensed power spectraldensity.
 25. The transceiver device of claim 23, wherein the processoris configured to determine the spectrum occupancy attributes of thenarrowband interference on the communication channel by performingoperations that include: computing a power spectral density of thewaveform: based on a discrete Fourier transform, or based on a fastFourier transform; and generating a spectrum usability mask byquantizing the power spectral density relative to a set of thresholdvalues.
 26. The transceiver device of claim 25, wherein the processor isconfigured to generate the spectrum usability mask by quantizing thepower spectral density relative to the set of threshold values byperforming operations that include: identifying a threshold level ofinterference power received by a known subcarrier that is not exceededwhen averaged over a known period of time.
 27. The transceiver device ofclaim 25, wherein the processor is configured to generate the spectrumusability mask by quantizing the power spectral density relative to theset of threshold values by performing operations that include:identifying upper and lower threshold limits of interference powerreceived by a known subcarrier such that, when the interference power isaveraged over a known period of time, a value of the averageinterference power is bounded by the upper and lower threshold limits.28. The transceiver device of claim 23, wherein the processor is furtherconfigured to: generate a demodulated data set by demodulating modulateddata carried by subcarriers in the waveform; and erase data carried bythe subcarriers of the waveform that include cochannel interference. 29.The transceiver device of claim 23, wherein the processor is furtherconfigured to: generate a demodulated data set by demodulating modulateddata carried by subcarriers in the waveform; determine whether thedemodulated data set includes a demodulated data packet that includes anuncorrected error; and erase the demodulated data packet in response todetermining that the demodulated data set includes the demodulated datapacket that includes the uncorrected error.
 30. The transceiver deviceof claim 23, wherein the processor is further configured to: identifypackets that are free of errors; maintain a first count of the number ofpackets received in the receiver device; and maintain a second count ofthe number of packets received error free in the receiver device. 31.The transceiver device of claim 23, wherein: the communication channelcomprises a plurality of discontiguous subchannels in the radiospectrum, the subchannels having arbitrary bandwidths; and thetransceiver device is configured to aggregate the plurality ofdiscontiguous subchannels to form a contiguous channel at anintermediate frequency.
 32. The transceiver device of claim 23, wherein:the intermediate frequency is zero Hz; and the processed signals arerepresented in complex baseband form.
 33. A method of communicating afile comprising a finite number of source data packets through afrequency division multiplexed wireless communication channel that ispartially occupied by narrowband interference, the method comprising:using, by a transceiver device, a fountain code to encode the sourcedata packets; transmitting, by the transceiver device to a receiverdevice, the encoded data packets using all subcarriers, regardless ofwhether they are encountering interference at the receiver; andcontinuing to transmit, by the transceiver device to the receiverdevice, the encoded packets until a notice of acknowledgement of filedelivery or a notice of failure of file delivery is received.
 34. Themethod of claim 33, further comprising: receiving encoded data packets;identifying the received packets that are free of errors; keeping afirst count of the number of received packets; and keeping a secondcount of the number of the received packets that are free of errors. 35.The method of claim 34, further comprising: decoding the file oftransmitted encoded data packets in response to determining that thesecond count exceeds a threshold.
 36. The method of claim 35, furthercomprising: abandoning the decoding attempts for the file in response todetermining that the first count exceeds a threshold value.
 37. Themethod of claim 33, further comprising: erasing a received packet basedon spectrum occupancy attributes of narrowband interference on acommunication channel at a location of the transceiver device.
 38. Themethod of claim 33, further comprising: performing a cyclic redundancycheck test on a demodulated packet; and erasing the demodulated packetin response to determining that the demodulated packet failed the cyclicredundancy check test.
 39. The method of claim 33, wherein the filefurther comprises information about the spectral occupancy ofinterference received by the transceiver device, and the method furthercomprises: broadcasting spectral occupancy information for reception bya plurality of other transceivers.
 40. The method of claim 33, whereinthe file further comprises user data, and the method further comprisesbroadcasting the file for reception by a plurality of receivingtransceivers having dissimilar interference spectral occupancies attheir locations.
 41. A transceiver device, comprising: a processorconfigured to: communicate a file comprising a finite number of sourcedata packets through a frequency division multiplexed wirelesscommunication channel that is partially occupied by narrowbandinterference by: using a fountain code to encode the source datapackets; and transmitting the encoded data packets using allsubcarriers, regardless of whether they are encountering interference atthe receiver; and continuing to transmit the encoded packets until anotice of acknowledgement of file delivery or a notice of failure offile delivery is received.
 42. The transceiver device of claim 41,wherein the processor is further configured to: receive encoded datapackets; identify the received packets that are free of errors; keep afirst count of the number of received packets; and keep a second countof the number of the received packets that are free of errors.
 43. Thetransceiver device of claim 42, wherein the processor is furtherconfigured to: decode the file of transmitted encoded data packets inresponse to determining that the second count exceeds a threshold. 44.The transceiver device of claim 43, wherein the processor is furtherconfigured to: abandon the decoding attempts for the file in response todetermining that the first count exceeds a threshold value.
 45. Thetransceiver device of claim 41, wherein the processor is furtherconfigured to: erase a received packet based on spectrum occupancyattributes of narrowband interference on a communication channel at alocation of the transceiver device.
 46. The transceiver device of claim41, wherein the processor is further configured to: perform a cyclicredundancy check test on a demodulated packet; and erase the demodulatedpacket in response to determining that the demodulated packet failed thecyclic redundancy check test.
 47. The transceiver device of claim 41,wherein the file further comprises information about the spectraloccupancy of interference received by the transceiver device, and theprocessor is further configured to: broadcasting spectral occupancyinformation for reception by a plurality of other transceivers.
 48. Thetransceiver device of claim 41, wherein the file further comprises userdata, and wherein the processor is further configured to: broadcast thefile for reception by a plurality of receiving transceivers havingdissimilar interference spectral occupancies at their locations.